$ git clone -n https://src.fedoraproject.org/rpms/R-XVector.git /var/lib/mock/f45-build-5961-345/root/chroot_tmpdir/scmroot/R-XVector
Cloning into '/var/lib/mock/f45-build-5961-345/root/chroot_tmpdir/scmroot/R-XVector'...
$ git fetch origin c18690b92defc1231c17f564e87c2587dfa1afbe:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-XVector
 * [new ref]         c18690b92defc1231c17f564e87c2587dfa1afbe -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c18690b Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild