$ git clone -n https://src.fedoraproject.org/rpms/f24-backgrounds.git /var/lib/mock/f45-build-8839-396/root/chroot_tmpdir/scmroot/f24-backgrounds
Cloning into '/var/lib/mock/f45-build-8839-396/root/chroot_tmpdir/scmroot/f24-backgrounds'...
$ git fetch origin 8a5f8c434cd6437cecbec29cb1c1984faeadc2f9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f24-backgrounds
 * [new ref]         8a5f8c434cd6437cecbec29cb1c1984faeadc2f9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 8a5f8c4 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild