UB: fix use of `warn` method instead of `warning` for outputing messages

gems/gitlab-backup-cli/lib/gitlab/backup/cli/targets/database.rb

@@ -94,7 +94,7 @@ def restore(destination_dir, _)
                   raise(::Backup::Error, "Source database file does not exist #{db_file_name}")
                 end
 
-                Gitlab::Backup::Cli::Output.warn(
+                Gitlab::Backup::Cli::Output.warning(
                   "Source backup for the database #{database_name} doesn't exist. Skipping the task"
                 )