Update inputs for test_source (<default_xs> is gone)
Update inputs for test_source (<default_xs> is gone)

smharper/openmc,samuelshaner/openmc,wbinventor/openmc,mit-crpg/openmc,mit-crpg/openmc,wbinventor/openmc,shikhar413/openmc,walshjon/openmc,samuelshaner/openmc,samuelshaner/openmc,paulromano/openmc,wbinventor/openmc,samuelshaner/openmc,johnnyliu27/openmc,liangjg/openmc,walshjon/openmc,paulromano/openmc,amandalund/openmc,paulromano/openmc,johnnyliu27/openmc,johnnyliu27/openmc,wbinventor/openmc,amandalund/openmc,bhermanmit/openmc,liangjg/openmc,paulromano/openmc,smharper/openmc,walshjon/openmc,mit-crpg/openmc,shikhar413/openmc,bhermanmit/openmc,mit-crpg/openmc,amandalund/openmc,liangjg/openmc,shikhar413/openmc,smharper/openmc,amandalund/openmc,johnnyliu27/openmc,smharper/openmc,walshjon/openmc,liangjg/openmc,shikhar413/openmc