$ git clone -n https://src.fedoraproject.org/rpms/R-rcmdcheck.git /var/lib/mock/f42-build-3530683-46321/root/chroot_tmpdir/scmroot/R-rcmdcheck
Cloning into '/var/lib/mock/f42-build-3530683-46321/root/chroot_tmpdir/scmroot/R-rcmdcheck'...
$ git fetch origin 4880419f5fd86923dfad5a3c49f94427202357f1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-rcmdcheck
 * [new ref]         4880419f5fd86923dfad5a3c49f94427202357f1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4880419 R-maint-sig mass rebuild