Python: Sample not working

Hi everyone,

This sample is not working

https://github.com/microsoft/agent-framework/blob/main/python/samples/02-agents/chat_client/chat_response_cancellation.py

Please fix it. Line 31 doesn't work.

Suggestion:
```python
task = asyncio.create_task(client.get_response(messages=[Message(role="user", text="Tell me a fantasy story.")]))
```

Thank you.
Regard


