Fix issue in getting current request through classmethod when served …

…through a different ASGI server (#2760)

sanic/asgi.py

@@ -175,6 +175,7 @@ async def create(
             instance.transport,
             sanic_app,
         )
+        request_class._current.set(instance.request)
         instance.request.stream = instance  # type: ignore
         instance.request_body = True
         instance.request.conn_info = ConnInfo(instance.transport)