rubocop noise: fixes FrozenStringLiteralComment

Adding the .ruby-verison file triggered previously un-run cops, specifically:

  This cop is designed to help upgrade to Ruby 3.0. It will add the
  comment `# frozen_string_literal: true` to the top of files to enable
  frozen string literals. Frozen string literals will be default in Ruby
  3.0. The comment will be added below a shebang and encoding comment. The
  frozen string literal comment is only valid in Ruby 2.3+.

More info on rubocop [Automatic-Corrections](https://github.com/bbatsov/rubocop/wiki/Automatic-Corrections)

test/controllers/admin/auth_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 module Admin

test/controllers/admin/profile_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 module Admin

test/controllers/admin/question_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 module Admin

test/controllers/admin/quiz_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 module Admin

test/controllers/admin/user_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 module Admin

test/controllers/admin_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AdminControllerTest < ActionDispatch::IntegrationTest

test/controllers/application_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class ApplicationControllerTest < ActionDispatch::IntegrationTest

test/controllers/candidate_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CandidateControllerTest < ActionDispatch::IntegrationTest

test/controllers/quiz_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuizControllerTest < ActionDispatch::IntegrationTest

test/controllers/recruiter_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class RecruiterControllerTest < ActionDispatch::IntegrationTest

test/controllers/review_controller_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class ReviewControllerTest < ActionDispatch::IntegrationTest

test/integration/question_attachments_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuestionAttachmentsTest < ActionDispatch::IntegrationTest

test/integration/question_flow_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuestionFlowTest < ActionDispatch::IntegrationTest

test/integration/question_live_coder_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuestionLiveCoderTest < ActionDispatch::IntegrationTest

test/mailers/candidate_mailer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CandidateMailerTest < ActionMailer::TestCase

test/mailers/previews/candidate_mailer_preview.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Preview all emails at http://localhost:3000/rails/mailers/candidate_mailer
 class CandidateMailerPreview < ActionMailer::Preview
   def welcome

test/mailers/previews/recruiter_mailer_preview.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Preview all emails at http://localhost:3000/rails/mailers/recruiter_mailer
 class RecruiterMailerPreview < ActionMailer::Preview
   def candidate_created

test/mailers/previews/reviewer_mailer_preview.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Preview all emails at http://localhost:3000/rails/mailers/reviewer_mailer
 class ReviewerMailerPreview < ActionMailer::Preview
   def candidate_submission

test/mailers/previews/user_mailer_preview.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Preview all emails at http://localhost:3000/rails/mailers/user_mailer
 class UserMailerPreview < ActionMailer::Preview
   def password_reset

test/mailers/recruiter_mailer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class RecruiterMailerTest < ActionMailer::TestCase

test/mailers/reviewer_mailer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class ReviewerMailerTest < ActionMailer::TestCase

test/mailers/user_mailer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class UserMailerTest < ActionMailer::TestCase

test/models/answer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AnswerTest < ActiveSupport::TestCase

test/models/candidate_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CandidateTest < ActiveSupport::TestCase

test/models/question_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuestionTest < ActiveSupport::TestCase

test/models/quiz_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuizTest < ActiveSupport::TestCase

test/models/user_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class UserTest < ActiveSupport::TestCase

test/services/crypt_serializer_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CryptSerializerTest < ActiveSupport::TestCase

test/services/skill_config_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class SkillConfigTest < ActiveSupport::TestCase

test/test_helper.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 ENV['RAILS_ENV'] ||= 'test'
 
 # https://github.com/colszowka/simplecov

test/test_helpers/answer_validatable.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class AnswerValidatable
   include ActiveModel::Validations
 

test/test_helpers/email_validatable.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class EmailValidatable
   include ActiveModel::Validations
   attr_accessor :email

test/test_helpers/input_options_validatable.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class InputOptionsValidatable
   include ActiveModel::Validations
   attr_accessor :input_type

test/validators/answer_format_validator/checkbox_other_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 # *_with_other answers expect a hash response:

test/validators/answer_format_validator/checkbox_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AnswerFormatValidatorTest < ActiveSupport::TestCase

test/validators/answer_format_validator/live_code_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AnswerFormatValidatorTest < ActiveSupport::TestCase

test/validators/answer_format_validator/radio_other_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 # *_with_other answers expect a hash answer:

test/validators/answer_format_validator/radio_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AnswerFormatValidatorTest < ActiveSupport::TestCase

test/validators/answer_format_validator/text_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class AnswerFormatValidatorTest < ActiveSupport::TestCase

test/validators/email_format_validator_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class EmailFormatValidatorTest < ActiveSupport::TestCase

test/validators/input_options_presence_validator_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class InputOptionsPresenceValidatorTest < ActiveSupport::TestCase

test/workers/candidate_quiz_question_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CandidateQuizQuestionTest < ActiveSupport::TestCase

test/workers/candidate_quiz_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class CandidateQuizTest < ActiveSupport::TestCase

test/workers/quiz_status_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class QuizStatusTest < ActiveSupport::TestCase

test/workers/reminder_test.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'test_helper'
 
 class ReminderTest < ActiveSupport::TestCase