Fix partition signature (#413)

django-stubs/utils/functional.pyi

@@ -56,4 +56,8 @@ class SimpleLazyObject(LazyObject):
     def __copy__(self) -> List[int]: ...
     def __deepcopy__(self, memo: Dict[Any, Any]) -> List[int]: ...
 
-def partition(predicate: Callable, values: List[Model]) -> Tuple[List[Model], List[Model]]: ...
+_PartitionMember = TypeVar("_PartitionMember")
+
+def partition(
+    predicate: Callable, values: List[_PartitionMember]
+) -> Tuple[List[_PartitionMember], List[_PartitionMember]]: ...