Enable frozen string for spec/routing

Partially addresses:

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

spec/routing/admin_routing_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 #       block_admin_user PUT    /admin/users/:id/block(.:format)       admin/users#block

spec/routing/environments_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'environments routing' do

spec/routing/group_routing_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe "Groups", "routing" do

spec/routing/import_routing_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 # Shared examples for a resource inside a Project

spec/routing/notifications_routing_spec.rb

+# frozen_string_literal: true
+
 require "spec_helper"
 
 describe "notifications routing" do

spec/routing/openid_connect_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 # oauth_discovery_keys      GET /oauth/discovery/keys(.:format)             doorkeeper/openid_connect/discovery#keys

spec/routing/project_routing_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe 'project routing' do

spec/routing/routing_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 # user                       GET    /users/:username/