Enable frozen string for spec/frontend

Partially addresses:

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

spec/frontend/fixtures/abuse_reports.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Admin::AbuseReportsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/admin_users.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Admin::UsersController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/application_settings.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Admin::ApplicationSettingsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/blob.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::BlobController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/boards.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::BoardsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/branches.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::BranchesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/clusters.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::ClustersController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/commit.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::CommitController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/deploy_keys.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::DeployKeysController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/groups.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Groups (JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/issues.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::IssuesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/jobs.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::JobsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/labels.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Labels (JavaScript fixtures)' do

spec/frontend/fixtures/merge_requests.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::MergeRequestsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/merge_requests_diffs.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::MergeRequests::DiffsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/pipeline_schedules.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::PipelineSchedulesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/pipelines.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::PipelinesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/projects.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Projects (JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/prometheus_service.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::ServicesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/raw.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Raw files', '(JavaScript fixtures)' do

spec/frontend/fixtures/search.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe SearchController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/services.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Projects::ServicesController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/sessions.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Sessions (JavaScript fixtures)' do

spec/frontend/fixtures/snippet.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe SnippetsController, '(JavaScript fixtures)', type: :controller do

spec/frontend/fixtures/todos.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'Todos (JavaScript fixtures)' do

spec/frontend/fixtures/u2f.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 context 'U2F' do