Enable even more frozen string in lib/gitlab

Enables frozens string for the following:

* lib/gitlab/conflict/**/*.rb
* lib/gitlab/cross_project_access/**/*.rb
* lib/gitlab/cycle_analytics/**/*.rb
* lib/gitlab/data_builder/**/*.rb
* lib/gitlab/database/**/*.rb
* lib/gitlab/dependency_linker/**/*.rb
* lib/gitlab/diff/**/*.rb
* lib/gitlab/downtime_check/**/*.rb
* lib/gitlab/email/**/*.rb
* lib/gitlab/etag_caching/**/*.rb

Partially addresses gitlab-org/gitlab-ce#47424.

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/gitlab/email/message/repository_push.rb b/lib/gitlab/email/message/repository_push.rb
index cd9d3a6483f..ec412e7a8b1 100644
--- a/lib/gitlab/email/message/repository_push.rb
+++ b/lib/gitlab/email/message/repository_push.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Message
@@ -116,7 +118,7 @@ module Gitlab
         end
 
         def subject
-          subject_text = '[Git]'
+          subject_text = ['[Git]']
           subject_text << "[#{project.full_path}]"
           subject_text << "[#{ref_name}]" if @action == :push
           subject_text << ' '
@@ -134,6 +136,8 @@ module Gitlab
             subject_action[0] = subject_action[0].capitalize
             subject_text << "#{subject_action} #{ref_type} #{ref_name}"
           end
+
+          subject_text.join
         end
       end
     end