$ git clone -n https://src.fedoraproject.org/rpms/f29-backgrounds.git /var/lib/mock/f45-build-8655-393/root/chroot_tmpdir/scmroot/f29-backgrounds
Cloning into '/var/lib/mock/f45-build-8655-393/root/chroot_tmpdir/scmroot/f29-backgrounds'...
$ git fetch origin e79a861ed9eeaf076db465dd14a32e475e7d6fb6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f29-backgrounds
 * [new ref]         e79a861ed9eeaf076db465dd14a32e475e7d6fb6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e79a861 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild