RAG Chain fails with TypeError

Hi

I have just copied your code in a notebook and tried to run as-is for a quick test.

However, this line fails to run:

`rag_chain = {"sessions": retriever, "question": RunnablePassthrough()} | prompt | llm`

with the following error:
```
TypeError: Expected a Runnable, callable or dict.Instead got an unsupported type:
```

As there is no version pinning in the `requirements.txt` file, I am curious if you can repro this same error with the latest version of langchain, or comment on which version works for you. Thanks.

Start with the notebook example containing the failing rag_chain expression and inspect requirements.txt, which currently has no version pinning. Reproduce the TypeError with the latest LangChain version, then determine and document the compatible version or dependency change needed for the example to run.

Written by the indexing model from the issue text.