Fix typo in docs websocket_async code example

Author: leszekhanusz

docs/code_examples/websockets_async.py

@@ -11,7 +11,7 @@ async def main():
     # Using `async with` on the client will start a connection on the transport
     # and provide a `session` variable to execute queries on this connection
     async with Client(
-        transport=sample_transport,
+        transport=transport,
         fetch_schema_from_transport=True,
         ) as session: