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/validators/answer_format_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class AnswerFormatValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     send(record.question.input_type, record, attribute, value)

app/validators/email_format_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class EmailFormatValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     # EMAIL regex test

app/validators/input_options_presence_validator.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class InputOptionsPresenceValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     return true unless record.input_type =~ /radio|check/i