Update crates/ty_python_semantic/resources/mdtest/attributes.md

Co-authored-by: Carl Meyer <carl@oddbird.net>

Author: mtshiba

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -2287,6 +2287,7 @@ class Base:
         return Sub()
 
 class Sub(Base):
+    # TODO invalid override error
     def flip(self) -> "Base":
         return Base()