Fix and allow classes with missing metaclasses (#9136)

stubs/peewee/peewee.pyi

@@ -1546,7 +1546,7 @@ class _BoundModelsContext(_callable_context_manager):
     def __enter__(self): ...
     def __exit__(self, exc_type, exc_val, exc_tb) -> None: ...
 
-class Model:
+class Model(metaclass=ModelBase):
     __data__: Incomplete
     __rel__: Incomplete
     def __init__(self, *args, **kwargs) -> None: ...