$ git clone -n https://src.fedoraproject.org/rpms/spherical-cow-backgrounds.git /var/lib/mock/f40-build-2374192-60416/root/chroot_tmpdir/scmroot/spherical-cow-backgrounds
Cloning into '/var/lib/mock/f40-build-2374192-60416/root/chroot_tmpdir/scmroot/spherical-cow-backgrounds'...
$ git fetch origin b666811604c540f82b58ff8a0e829f6f2644205d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/spherical-cow-backgrounds
 * [new ref]         b666811604c540f82b58ff8a0e829f6f2644205d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b666811 Update spherical-cow-backgrounds.spec