afced5b405
$CI_COMMIT_REF_NAME can be a branch name or a tag, depending on the pipeline, but our checkout script only deals with the former at the moment. Address this by rather than looking for a remote branch name, just try to fetch the ref like we do for merge request pipelines. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1630>