Fix return type of asyncio.Queue.join (#4751)

Fixes #4750

stdlib/3/asyncio/queues.pyi

@@ -27,7 +27,7 @@ class Queue(Generic[_T]):
     def put_nowait(self, item: _T) -> None: ...
     async def get(self) -> _T: ...
     def get_nowait(self) -> _T: ...
-    async def join(self) -> bool: ...
+    async def join(self) -> None: ...
     def task_done(self) -> None: ...
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, type: Any) -> GenericAlias: ...