$ git clone -n https://src.fedoraproject.org/rpms/f25-backgrounds.git /var/lib/mock/f45-build-8582-391/root/chroot_tmpdir/scmroot/f25-backgrounds
Cloning into '/var/lib/mock/f45-build-8582-391/root/chroot_tmpdir/scmroot/f25-backgrounds'...
$ git fetch origin a1ddbf622ba1660defa589fbb6cf998cc9e527f0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f25-backgrounds
 * [new ref]         a1ddbf622ba1660defa589fbb6cf998cc9e527f0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a1ddbf6 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild