Fix more incompatibility with python38

Author: taeold

src/functions_framework/aio/__init__.py

@@ -17,7 +17,7 @@
 import inspect
 import os
 
-from typing import Any, Awaitable, Callable, Dict, Union
+from typing import Any, Awaitable, Callable, Dict, Tuple, Union
 
 from cloudevents.http import from_http
 from cloudevents.http.event import CloudEvent
@@ -44,7 +44,7 @@
     Response,  # Functions can return a full Starlette Response object
     str,  # Str returns are wrapped in Response(result)
     Dict[Any, Any],  # Dict returns are wrapped in JSONResponse(result)
-    tuple[Any, int],  # Flask-style (content, status_code) supported
+    Tuple[Any, int],  # Flask-style (content, status_code) supported
     None,  # None raises HTTPException
 ]