$ git clone -n https://src.fedoraproject.org/rpms/R-sys.git /var/lib/mock/f38-build-720696-97830/root/chroot_tmpdir/scmroot/R-sys
Cloning into '/var/lib/mock/f38-build-720696-97830/root/chroot_tmpdir/scmroot/R-sys'...
$ git fetch origin d52a107a74db1cc40290117a00df9d014cfd8cda:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-sys
 * [new ref]         d52a107a74db1cc40290117a00df9d014cfd8cda -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d52a107 R-maint-sig mass rebuild