Merge branch 'frozen-string-enable-lib-gitlab-middleware' into 'master'

Enable frozen string for middleware specs

See merge request gitlab-org/gitlab!20692

spec/lib/gitlab/middleware/go_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Middleware::Go do
@@ -25,7 +27,7 @@ describe Gitlab::Middleware::Go do
     describe 'when go-get=1' do
       before do
         env['QUERY_STRING'] = 'go-get=1'
-        env['PATH_INFO'] = "/#{path}"
+        env['PATH_INFO'] = +"/#{path}"
       end
 
       shared_examples 'go-get=1' do |enabled_protocol:|