Merge branch 'frozen-string-enable-spec-mailers' into 'master'

Partially addresses:

See merge request gitlab-org/gitlab!18854

spec/mailers/abuse_report_mailer_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe AbuseReportMailer do

spec/mailers/emails/merge_requests_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'email_spec'
 

spec/mailers/emails/pages_domains_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'email_spec'
 

spec/mailers/emails/profile_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'email_spec'
 

spec/mailers/notify_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'email_spec'
 

spec/mailers/repository_check_mailer_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe RepositoryCheckMailer do