Add __new__ to tuple stub (#2092)

Closes: #2091

Apply suggestions from https://github.com/python/typeshed/pull/2092

stdlib/3/builtins.pyi

@@ -582,6 +582,7 @@ class slice:
     def indices(self, len: int) -> Tuple[int, int, int]: ...
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
+    def __new__(cls: Type[_T], iterable: Iterable[_T_co] = ...) -> _T: ...
     def __init__(self, iterable: Iterable[_T_co] = ...) -> None: ...
     def __len__(self) -> int: ...
     def __contains__(self, x: object) -> bool: ...