$ git clone -n https://src.fedoraproject.org/rpms/R-gmp.git /var/lib/mock/f45-build-6146-346/root/chroot_tmpdir/scmroot/R-gmp
Cloning into '/var/lib/mock/f45-build-6146-346/root/chroot_tmpdir/scmroot/R-gmp'...
$ git fetch origin 1e76f18d78200c4c00d24f22d1dcbb3a9edef565:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-gmp
 * [new ref]         1e76f18d78200c4c00d24f22d1dcbb3a9edef565 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1e76f18 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild