Make Timer args less restrictive (#3007)

Closes #3004

stdlib/2and3/threading.pyi

@@ -164,11 +164,11 @@ class Event:
 class Timer(Thread):
     if sys.version_info >= (3,):
         def __init__(self, interval: float, function: Callable[..., None],
-                     args: Optional[List[Any]] = ...,
+                     args: Optional[Iterable[Any]] = ...,
                      kwargs: Optional[Mapping[str, Any]] = ...) -> None: ...
     else:
         def __init__(self, interval: float, function: Callable[..., None],
-                     args: List[Any] = ...,
+                     args: Iterable[Any] = ...,
                      kwargs: Mapping[str, Any] = ...) -> None: ...
     def cancel(self) -> None: ...