Change a test case slightly

Author: davidhalter

conformance/tests/generics_self_advanced.py

@@ -44,4 +44,4 @@ def method3(cls) -> None:
         assert_type(cls.method1(), Self)
 
 ClassB.a # E: Ambigous access
-ClassB.a = ClassB.method1() # E: Ambigous write
+Parent.a = ClassB.method1() # E: Ambigous write