Tests: fix some tests passing even if there are Python errors

Blender was not configured to exit with non-zero return code on Python errors.
A bunch of tests worked around this but not all. This removes the need for such
workarounds.

tests/python/bl_mesh_modifiers.py

@@ -842,17 +842,7 @@ if __name__ == "__main__":
         print("Load Handler:", bpy.data.filepath)
         if load_handler.first is False:
             bpy.app.handlers.scene_update_post.remove(load_handler)
-            try:
-                main()
-                import sys
-                sys.exit(0)
-            except:
-                import traceback
-                traceback.print_exc()
-
-                # import sys
-                # sys.exit(1)  # comment to debug
-
+            main()
         else:
             load_handler.first = False