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)

app/controllers/admin/auth_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class AuthController < AdminController
     skip_before_action :authorize_admin

app/controllers/admin/profile_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class ProfileController < AdminController
     def view

app/controllers/admin/question_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class QuestionController < AdminController
     def index

app/controllers/admin/quiz_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class QuizController < AdminController
     def index

app/controllers/admin/user_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Admin
   class UserController < AdminController
     def index

app/controllers/admin_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class AdminController < ApplicationController
   layout 'admin'
   before_action :authorize_admin

app/controllers/application_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ApplicationController < ActionController::Base
   protect_from_forgery with: :exception
 

app/controllers/candidate_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class CandidateController < ApplicationController
   before_action :authorize_candidate, except: [:login, :validate, :live_coder]
   before_action :send_to_oops, only: [:login]

app/controllers/quiz_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class QuizController < ApplicationController
   before_action :authorize_candidate
 

app/controllers/recruiter_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class RecruiterController < ApplicationController
   before_action :authorize_recruiter, except: [:login, :auth]
 

app/controllers/review_controller.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class ReviewController < ApplicationController
   before_action :authorize_reviewer, except: [:login, :auth]