$ git clone -n https://src.fedoraproject.org/rpms/root.git /var/lib/mock/f39-build-1867287-42577/root/chroot_tmpdir/scmroot/root
Cloning into '/var/lib/mock/f39-build-1867287-42577/root/chroot_tmpdir/scmroot/root'...
$ git fetch origin 59989efa5f4087c1dd7b9eb3d4f660cd78c20675:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/root
 * [new ref]         59989efa5f4087c1dd7b9eb3d4f660cd78c20675 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 59989ef Update to 6.30.00