$ git clone -n https://src.fedoraproject.org/rpms/R-gh.git /var/lib/mock/f40-build-1944439-25177/root/chroot_tmpdir/scmroot/R-gh
Cloning into '/var/lib/mock/f40-build-1944439-25177/root/chroot_tmpdir/scmroot/R-gh'...
$ git fetch origin 6d79455f0a128b8b93b55bcccf657dec2a868c51:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-gh
 * [new ref]         6d79455f0a128b8b93b55bcccf657dec2a868c51 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6d79455 R-maint-sig mass rebuild