$ git clone -n https://src.fedoraproject.org/rpms/fgrun.git /var/lib/mock/f39-build-1506583-35201/root/chroot_tmpdir/scmroot/fgrun
Cloning into '/var/lib/mock/f39-build-1506583-35201/root/chroot_tmpdir/scmroot/fgrun'...
$ git fetch origin 3160267b0db8a8465f91c305394ffa2e233ddf0d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/fgrun
 * [new ref]         3160267b0db8a8465f91c305394ffa2e233ddf0d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3160267 rebuild with newer SimGear