Update openmc/mgxs/mgxs.py
Update openmc/mgxs/mgxs.py

Co-authored-by: Giud <6d5f5fac4a74debab696d70693084d9f0f9e2999@gmail.com>
mit-crpg/openmc,mit-crpg/openmc,walshjon/openmc,mit-crpg/openmc,amandalund/openmc,shikhar413/openmc,amandalund/openmc,amandalund/openmc,paulromano/openmc,paulromano/openmc,walshjon/openmc,liangjg/openmc,liangjg/openmc,paulromano/openmc,liangjg/openmc,paulromano/openmc,walshjon/openmc,mit-crpg/openmc,amandalund/openmc,walshjon/openmc,liangjg/openmc,shikhar413/openmc,shikhar413/openmc,shikhar413/openmc