$ git clone -n https://src.fedoraproject.org/rpms/linbox.git /var/lib/mock/f42-build-3356263-45027/root/chroot_tmpdir/scmroot/linbox
Cloning into '/var/lib/mock/f42-build-3356263-45027/root/chroot_tmpdir/scmroot/linbox'...
$ git fetch origin 5ce2594ae8752966b64055266d63e6a8621ffc50:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/linbox
 * [new ref]         5ce2594ae8752966b64055266d63e6a8621ffc50 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5ce2594 Rebuilt for givaro 4.2.1