Backup::Database class does not have config anymore since in gitlab it's now possible to configure many databases.
We need now to get config from base_model: https://lab.nexedi.com/nexedi/gitlab-ce/-/blob/v15.11.13-nxd/lib/gitlab/database/each_database.rb#L39 If more than one databases gitlab can backup and restore them: https://lab.nexedi.com/nexedi/gitlab-ce/-/blob/v15.11.13-nxd/lib/backup/database.rb#L75 This feature is not supported for now.
For our gitlab, we only use main database so base_model count is always 1. This
patch will raise if there is more than one databases configured because gitlab-backup
cannot handle it for now.