$ git clone -n https://src.fedoraproject.org/rpms/f42-backgrounds.git /var/lib/mock/f45-build-8619-392/root/chroot_tmpdir/scmroot/f42-backgrounds
Cloning into '/var/lib/mock/f45-build-8619-392/root/chroot_tmpdir/scmroot/f42-backgrounds'...
$ git fetch origin a39e481a0636d92ce37dafad87aefa21d0b42784:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f42-backgrounds
 * [new ref]         a39e481a0636d92ce37dafad87aefa21d0b42784 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a39e481 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild