Bugfix ensure websocket disconnect cancels the connection's tasks

The return would skip paste the cancel call, resulting in the nursery
not being cancelled and hence the app potentially running after
disconnection.

src/quart_trio/asgi.py

@@ -59,7 +59,7 @@ async def handle_messages(  # type: ignore
             if event["type"] == "websocket.receive":
                 await self.send_channel.send(event.get("bytes") or event["text"])
             elif event["type"] == "websocket.disconnect":
-                return
+                break
         nursery.cancel_scope.cancel()
 
     def _create_websocket_from_scope(self, send: Callable) -> Websocket:

tests/test_asgi.py

@@ -0,0 +1,26 @@
+import pytest
+import trio
+
+from quart_trio.app import QuartTrio
+from quart_trio.asgi import TrioASGIWebsocketConnection
+
+
+@pytest.mark.trio
+async def test_websocket_complete_on_disconnect() -> None:
+    scope = {
+        "asgi": {"version": "3"},
+        "headers": [(b"host", b"quart")],
+        "http_version": "1.1",
+        "method": "GET",
+        "scheme": "wss",
+        "path": "ws://quart/path",
+        "query_string": b"",
+        "subprotocols": [],
+        "extensions": {"websocket.http.response": {}},
+    }
+    connection = TrioASGIWebsocketConnection(QuartTrio(__name__), scope)
+    send_channel, receive_channel = trio.open_memory_channel(0)
+    async with trio.open_nursery() as nursery:
+        nursery.start_soon(connection.handle_messages, nursery, receive_channel.receive)
+        await send_channel.send({"type": "websocket.disconnect"})
+    assert nursery.cancel_scope.cancelled_caught