Add __init__ to OrderedSet (#381)

django-stubs/utils/datastructures.pyi

@@ -22,6 +22,7 @@ _V = TypeVar("_V")
 
 class OrderedSet(MutableSet[_K]):
     dict: Dict[_K, None] = ...
+    def __init__(self, iterable: Optional[Iterable[_K]] = ...) -> None: ...
     def __contains__(self, item: object) -> bool: ...
     def __iter__(self) -> Iterator[_K]: ...
     def __len__(self) -> int: ...