Streaming example missing `stream=True` in chat.completions.create()

### Description

While following the streaming example, the API call does not enable streaming, which causes the event iteration code to fail.

### Location

File: chat_history_stream.py

### Problem

The example code currently contains:

```python
response = client.chat.completions.create(
    model=MODEL_NAME,
    messages=messages,
    temperature=0.7,
)