Agent server langgraph sample has error in Teams coroutine 'AsyncItems.list' was never awaited

Deployed and published to M365, the calculator agent langgraph sample fails to respond from Teams.

```
2026-02-23T16:30:48.0907702Z stderr F /usr/local/lib/python3.12/site-packages/azure/ai/agentserver/langgraph/models/response_api_default_converter.py:251: RuntimeWarning: coroutine 'AsyncItems.list' was never awaited
2026-02-23T16:30:48.0908101Z stderr F async for item in openai_client.conversations.items.list(conversation_id):
2026-02-23T16:30:48.0908266Z stderr F RuntimeWarning: Enable tracemalloc to get the object allocation traceback
2026-02-23T16:30:48.0910872Z stdout F 2026-02-23 16:30:48,090 - azure.ai.agentserver - WARNING - Failed to fetch historical items for conversation conv_d3347f439cc3dff300BesVmRU3eoP5dKq9i0i2Dz8wGRFYziuW: 'async for' requires an object with __aiter__ method, got coroutine
2026-02-23T16:30:48.0910960Z stdout F Traceback (most recent call last):
2026-02-23T16:30:48.0910995Z stdout F File "/usr/local/lib/python3.12/site-packages/azure/ai/agentserver/langgraph/models/response_api_default_converter.py", line 251, in _fetch_historical_items
2026-02-23T16:30:48.0911012Z stdout F async for item in openai_client.conversations.items.list(conversation_id):
2026-02-23T16:30:48.0911056Z stdout F ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2026-02-23T16:30:48.0911072Z stdout F TypeError: 'async for' requires an object with __aiter__ method, got coroutine
```

`azure-ai-agentserver-langgraph==1.0.0b13`.

*b12 has other issues failing because of something related to tool call IDs.

Here is the sample: https://github.com/microsoft-foundry/foundry-samples/tree/main/samples/python/hosted-agents/langgraph/calculator-agent

It will respond in the playground, but fails from Teams.