Typing: loose _Message from dict to MutableMapping

Resolves encode#2832

Author: YDX-2147483647

httpx/_transports/asgi.py

@@ -14,11 +14,9 @@
     Event = typing.Union[asyncio.Event, trio.Event]
 
 
-_Message = typing.Dict[str, typing.Any]
+_Message = typing.MutableMapping[str, typing.Any]
 _Receive = typing.Callable[[], typing.Awaitable[_Message]]
-_Send = typing.Callable[
-    [typing.Dict[str, typing.Any]], typing.Coroutine[None, None, None]
-]
+_Send = typing.Callable[[_Message], typing.Coroutine[None, None, None]]
 _ASGIApp = typing.Callable[
     [typing.Dict[str, typing.Any], _Receive, _Send], typing.Coroutine[None, None, None]
 ]
@@ -137,7 +135,7 @@ async def receive() -> typing.Dict[str, typing.Any]:
                 return {"type": "http.request", "body": b"", "more_body": False}
             return {"type": "http.request", "body": body, "more_body": True}
 
-        async def send(message: typing.Dict[str, typing.Any]) -> None:
+        async def send(message: _Message) -> None:
             nonlocal status_code, response_headers, response_started
 
             if message["type"] == "http.response.start":