$ git clone -n https://src.fedoraproject.org/rpms/R-rex.git /var/lib/mock/f45-build-6369-348/root/chroot_tmpdir/scmroot/R-rex
Cloning into '/var/lib/mock/f45-build-6369-348/root/chroot_tmpdir/scmroot/R-rex'...
$ git fetch origin e2b865704b6c1468051a93156bf236233a7e0e61:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-rex
 * [new ref]         e2b865704b6c1468051a93156bf236233a7e0e61 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e2b8657 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild