$ git clone -n https://src.fedoraproject.org/rpms/root.git /var/lib/mock/f42-build-864575-172456/root/chroot_tmpdir/scmroot/root
Cloning into '/var/lib/mock/f42-build-864575-172456/root/chroot_tmpdir/scmroot/root'...
$ git fetch origin 75f062bccd02b4f92a9d9b5c8dc84dce6b6461b4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/root
 * [new ref]         75f062bccd02b4f92a9d9b5c8dc84dce6b6461b4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 75f062b Update to 6.34.02