There is no type.__prepare__ so we cannot detect a false negative

We used to pretend that this method existed and that it was an override
when in fact it is not. We could check __prepare__ based on this
special knowledge.

python/testData/inspections/PyMethodOverridingInspection/DunderPrepare.py

@@ -1,6 +1,6 @@
 class MyType1(type):
     @staticmethod
-    def __prepare__<warning descr="Signature of method 'MyType1.__prepare__()' does not match signature of base method in class 'type'">(metacls, name)</warning>:
+    def __prepare__(metacls, name):
         return {}