$ git clone -n https://src.fedoraproject.org/rpms/R-data.table.git /var/lib/mock/f40-build-1930427-25111/root/chroot_tmpdir/scmroot/R-data.table
Cloning into '/var/lib/mock/f40-build-1930427-25111/root/chroot_tmpdir/scmroot/R-data.table'...
$ git fetch origin 5903ca8a5a81c5395cea0dfc1e6f33dde4cc8d1a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-data.table
 * [new ref]         5903ca8a5a81c5395cea0dfc1e6f33dde4cc8d1a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5903ca8 Update to latest version