$ git clone -n https://src.fedoraproject.org/rpms/mathicgb.git /var/lib/mock/f39-build-1849765-42222/root/chroot_tmpdir/scmroot/mathicgb
Cloning into '/var/lib/mock/f39-build-1849765-42222/root/chroot_tmpdir/scmroot/mathicgb'...
$ git fetch origin b897ef97b0e0410aee679511e90e9004f17bda9e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mathicgb
 * [new ref]         b897ef97b0e0410aee679511e90e9004f17bda9e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b897ef9 Update to latest upstream snapshot