Python: Fix: streaming Response Example in ollama_with_openai_chat_client

[Ceciile]

Motivation and Context

Ollama_with_openai_chat_client.py cannot run correctly.

The error :
TypeError: 'async for' requires an object with aiter method, got coroutine

Description

Use good attribute of 'ChatAgent' object

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Ceciile]

The first time, Code Qulity Check failed on pre-commit, but I found in your official doc "run-stream"