fix safe_task type hint for Python 3.8

Author: miguelgrinberg

elasticsearch/compat.py

@@ -106,7 +106,7 @@ def run() -> None:
 
 
 @asynccontextmanager
-async def safe_task(coro: Coroutine[Any, Any, Any]) -> AsyncIterator[asyncio.Task[Any]]:
+async def safe_task(coro: Coroutine[Any, Any, Any]) -> "AsyncIterator[asyncio.Task[Any]]":
     """Run a background task within a context manager block.
 
     The task is awaited when the block ends.