$ git clone -n https://src.fedoraproject.org/rpms/f31-backgrounds.git /var/lib/mock/f45-build-8594-391/root/chroot_tmpdir/scmroot/f31-backgrounds
Cloning into '/var/lib/mock/f45-build-8594-391/root/chroot_tmpdir/scmroot/f31-backgrounds'...
$ git fetch origin e8feaf78385c57913613e52d322af73a6df5cdc4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f31-backgrounds
 * [new ref]         e8feaf78385c57913613e52d322af73a6df5cdc4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e8feaf7 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild