$ git clone -n https://src.fedoraproject.org/rpms/HepMC3.git /var/lib/mock/f39-build-1878237-42744/root/chroot_tmpdir/scmroot/HepMC3
Cloning into '/var/lib/mock/f39-build-1878237-42744/root/chroot_tmpdir/scmroot/HepMC3'...
$ git fetch origin 9a4a5b4a8a895a3446903f6830d262216addb282:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/HepMC3
 * [new ref]         9a4a5b4a8a895a3446903f6830d262216addb282 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9a4a5b4 Rebuild for root 6.30