Enable frozen string in app/serializers/**/*.rb

Partially addresses #47424.

app/serializers/analytics_build_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsBuildEntity < Grape::Entity
   include RequestAwareEntity
   include EntityDateHelper

app/serializers/analytics_build_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsBuildSerializer < BaseSerializer
   entity AnalyticsBuildEntity
 end

app/serializers/analytics_commit_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsCommitEntity < CommitEntity
   include EntityDateHelper

app/serializers/analytics_commit_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsCommitSerializer < BaseSerializer
   entity AnalyticsCommitEntity
 end

app/serializers/analytics_generic_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsGenericSerializer < BaseSerializer
   def represent(resource, opts = {})
     resource.symbolize_keys!

app/serializers/analytics_issue_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsIssueEntity < Grape::Entity
   include RequestAwareEntity
   include EntityDateHelper

app/serializers/analytics_issue_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsIssueSerializer < AnalyticsGenericSerializer
   entity AnalyticsIssueEntity
 end

app/serializers/analytics_merge_request_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsMergeRequestEntity < AnalyticsIssueEntity
   expose :state

app/serializers/analytics_merge_request_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsMergeRequestSerializer < AnalyticsGenericSerializer
   entity AnalyticsMergeRequestEntity
 end

app/serializers/analytics_stage_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsStageEntity < Grape::Entity
   include EntityDateHelper

app/serializers/analytics_stage_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsStageSerializer < BaseSerializer
   entity AnalyticsStageEntity
 end

app/serializers/analytics_summary_entity.rb

+# frozen_string_literal: true
+
 class AnalyticsSummaryEntity < Grape::Entity
   expose :value, safe: true
   expose :title

app/serializers/analytics_summary_serializer.rb

+# frozen_string_literal: true
+
 class AnalyticsSummarySerializer < BaseSerializer
   entity AnalyticsSummaryEntity
 end

app/serializers/award_emoji_entity.rb

+# frozen_string_literal: true
+
 class AwardEmojiEntity < Grape::Entity
   expose :name
   expose :user, using: API::Entities::UserSafe

app/serializers/base_serializer.rb

+# frozen_string_literal: true
+
 class BaseSerializer
   attr_reader :params

app/serializers/blob_entity.rb

+# frozen_string_literal: true
+
 class BlobEntity < Grape::Entity
   include RequestAwareEntity

app/serializers/build_action_entity.rb

+# frozen_string_literal: true
+
 class BuildActionEntity < Grape::Entity
   include RequestAwareEntity

app/serializers/build_artifact_entity.rb

+# frozen_string_literal: true
+
 class BuildArtifactEntity < Grape::Entity
   include RequestAwareEntity

app/serializers/build_details_entity.rb

+# frozen_string_literal: true
+
 class BuildDetailsEntity < JobEntity
   expose :coverage, :erased_at, :duration
   expose :tag_list, as: :tags

app/serializers/build_metadata_entity.rb

+# frozen_string_literal: true
+
 class BuildMetadataEntity < Grape::Entity
   expose :timeout_human_readable
   expose :timeout_source do |metadata|