$ git clone -n https://src.fedoraproject.org/rpms/mathicgb.git /var/lib/mock/f42-build-side-1-3536512-46558/root/chroot_tmpdir/scmroot/mathicgb
Cloning into '/var/lib/mock/f42-build-side-1-3536512-46558/root/chroot_tmpdir/scmroot/mathicgb'...
$ git fetch origin bb5af6ceaf59ebe0f2eceb9a5be6227e0d7e73cb:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mathicgb
 * [new ref]         bb5af6ceaf59ebe0f2eceb9a5be6227e0d7e73cb -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at bb5af6c Update to latest upstream snapshot