$ git clone -n https://src.fedoraproject.org/rpms/rootfiles.git /var/lib/mock/f45-build-34609-688/root/chroot_tmpdir/scmroot/rootfiles
Cloning into '/var/lib/mock/f45-build-34609-688/root/chroot_tmpdir/scmroot/rootfiles'...
$ git fetch origin 13485d5c1106b82cfb53bcc1323ba551ad626922:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rootfiles
 * [new ref]         13485d5c1106b82cfb53bcc1323ba551ad626922 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 13485d5 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild