Enable frozen string for spec/uploaders

Partially addresses:

https://gitlab.com/gitlab-org/gitlab/issues/27703

spec/uploaders/attachment_uploader_spec.rb

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

spec/uploaders/avatar_uploader_spec.rb

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

spec/uploaders/external_diff_uploader_spec.rb

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

spec/uploaders/file_mover_spec.rb

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

spec/uploaders/file_uploader_spec.rb

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

spec/uploaders/gitlab_uploader_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'carrierwave/storage/fog'
 

spec/uploaders/import_export_uploader_spec.rb

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

spec/uploaders/job_artifact_uploader_spec.rb

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

spec/uploaders/lfs_object_uploader_spec.rb

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

spec/uploaders/namespace_file_uploader_spec.rb

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

spec/uploaders/object_storage_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 require 'carrierwave/storage/fog'
 

spec/uploaders/personal_file_uploader_spec.rb

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

spec/uploaders/records_uploads_spec.rb

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

spec/uploaders/uploader_helper_spec.rb

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

spec/uploaders/workers/object_storage/background_move_worker_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe ObjectStorage::BackgroundMoveWorker do

spec/uploaders/workers/object_storage/migrate_uploads_worker_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe ObjectStorage::MigrateUploadsWorker, :sidekiq do