Skip non-Newtonian examples in CI (too expensive, no golden files)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sbryngelson

toolchain/mfc/test/cases.py

@@ -1541,6 +1541,8 @@ def foreach_example():
                 "3D_IGR_33jet",
                 "1D_multispecies_diffusion",
                 "2D_ibm_stl_MFCCharacter",
+                "2D_lid_driven_cavity_nn",
+                "2D_poiseuille_nn",
             ]
             if path in casesToSkip:
                 continue