Rename `builds` in backup scripts to `jobs`

Missing from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8787. Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/27805.

• Backup script https://gitlab.com/gitlab-org/gitlab-ce/blob/48cc684d49230232594c4e8c3f84ccec0023787f/lib/backup/builds.rb
• Backup restore https://gitlab.com/gitlab-org/gitlab-ce/blob/059f47b6ba09ae1a6b1dbfc2debf82064d8793fc/doc/raketasks/backup_restore.md#exclude-specific-directories-from-the-backup