Set permissions of backup dir to g+s

lib/backup/repository.rb

@@ -54,7 +54,8 @@ module Backup
         # Move repos dir to 'repositories.old' dir
         bk_repos_path = File.join(path, '..', 'repositories.old.' + Time.now.to_i.to_s)
         FileUtils.mv(path, bk_repos_path)
-        FileUtils.mkdir_p(path)
+        # This is expected from gitlab:check
+        FileUtils.mkdir_p(path, mode: 2770)
       end
       Project.find_each(batch_size: 1000) do |project|