Add asyncio.staggered.__all__ (#7274)

stdlib/asyncio/staggered.pyi

@@ -2,6 +2,8 @@ from typing import Any, Awaitable, Callable, Iterable
 
 from . import events
 
+__all__ = ("staggered_race",)
+
 async def staggered_race(
     coro_fns: Iterable[Callable[[], Awaitable[Any]]], delay: float | None, *, loop: events.AbstractEventLoop | None = ...
 ) -> tuple[Any, int | None, list[Exception | None]]: ...