$ git clone -n https://src.fedoraproject.org/rpms/f28-backgrounds.git /var/lib/mock/f40-build-1995981-43964/root/chroot_tmpdir/scmroot/f28-backgrounds
Cloning into '/var/lib/mock/f40-build-1995981-43964/root/chroot_tmpdir/scmroot/f28-backgrounds'...
$ git fetch origin f321a21ce4eb2430d963fbd590c870527e244a5a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f28-backgrounds
 * [new ref]         f321a21ce4eb2430d963fbd590c870527e244a5a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f321a21 Rebuilt for https://fedoraproject.org/wiki/Fedora_39_Mass_Rebuild