Update test case

Author: JukkaL

mypyc/test-data/irbuild-classes.test

@@ -1375,7 +1375,8 @@ class BadUse():  # E: native_class must be used with True or False only
 from mypy_extensions import mypyc_attr
 
 @mypyc_attr(native_class=True)
-class M(type):  # E: Inheriting from most builtin types is unimplemented
+class M(type):  # E: Inheriting from most builtin types is unimplemented \
+                # N: Potential workaround: @mypy_extensions.mypyc_attr(native_class=False)
     pass
 
 @mypyc_attr(native_class=True)