Enable frozen string literals.

Make all string literals immutable by default.

app/controllers/maintenance/user/count_fixes_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Maintenance
   module User
     class CountFixesController < ApplicationController

app/controllers/maintenance/user/deletions_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Maintenance
   module User
     class DeletionsController < ApplicationController

app/controllers/maintenance/user/email_notifications_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Maintenance
   module User
     class EmailNotificationsController < ApplicationController