$ git clone -n https://src.fedoraproject.org/rpms/heisenbug-backgrounds.git /var/lib/mock/f40-build-2246505-53819/root/chroot_tmpdir/scmroot/heisenbug-backgrounds
Cloning into '/var/lib/mock/f40-build-2246505-53819/root/chroot_tmpdir/scmroot/heisenbug-backgrounds'...
$ git fetch origin d66715f7a2a7e38936858f8ac1c7dddfa887e554:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/heisenbug-backgrounds
 * [new ref]         d66715f7a2a7e38936858f8ac1c7dddfa887e554 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d66715f Orphaned for 6+ weeks