$ git clone -n https://src.fedoraproject.org/rpms/f29-backgrounds.git /var/lib/mock/f41-build-3152232-40629/root/chroot_tmpdir/scmroot/f29-backgrounds
Cloning into '/var/lib/mock/f41-build-3152232-40629/root/chroot_tmpdir/scmroot/f29-backgrounds'...
$ git fetch origin 403c64db77de197924b78dff6ee686ded6fa93a6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f29-backgrounds
 * [new ref]         403c64db77de197924b78dff6ee686ded6fa93a6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 403c64d Fix build on f40+