Merge branch 'frozen-string-vestigial' into 'master'

Enable frozen string in newly added files

See merge request gitlab-org/gitlab-ce!20763

app/uploaders/import_export_uploader.rb

+# frozen_string_literal: true
+
 class ImportExportUploader < AttachmentUploader
   EXTENSION_WHITELIST = %w[tar.gz].freeze

app/workers/concerns/each_shard_worker.rb

+# frozen_string_literal: true
+
 module EachShardWorker
   extend ActiveSupport::Concern
   include ::Gitlab::Utils::StrongMemoize

app/workers/delete_diff_files_worker.rb

+# frozen_string_literal: true
+
 class DeleteDiffFilesWorker
   include ApplicationWorker

app/workers/repository_check/dispatch_worker.rb

+# frozen_string_literal: true
+
 module RepositoryCheck
   class DispatchWorker
     include ApplicationWorker

changelogs/unreleased/frozen-string-vestigial.yml

+---
+title: Enable frozen string in newly added files to previously processed directories
+merge_request: 20763
+author: gfyoung
+type: performance