docs: fix jupyter notebook steps

[karthitect]

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Fixes #137 🦕

[rahul2393]

/gcbrun

[rahul2393]

@averikitsch Can you please help with one more approval on this PR
Context: b/431025682

[rahul2393]

@averikitsch
I see these errors in checks

E           google.api_core.exceptions.NotFound: 404 Publisher Model `projects/langchain-spanner-testing/locations/us-central1/publishers/google/models/gemini-1.5-flash-002` was not found or your project does not have access to it. Please ensure you are using a valid model version. For more information, see: https://cloud.google.com/vertex-ai/generative-ai/docs/learn/model-versions
>           raise exceptions.from_grpc_error(exc) from exc
        except grpc.RpcError as exc:
            return callable_(*args, **kwargs)
        try:
    def error_remapped_callable(*args, **kwargs):
    @functools.wraps(callable_)

kwargs = {'metadata': [('x-goog-request-params', 'model=projects/langchain-spanner-testing/locations/us-central1/publishers/goo...ython/3.12.12 grpc/1.76.0 gax/2.28.1 gccl/2.0.27-langchain-google-vertexai/2.0.27-ChatVertexAI_gemini-1.5-flash-002')]}
,)

[averikitsch]

Can you remove the outputs to ensure this is a clean view?

[averikitsch]

@rahul2393 can you update the tests that use the outdated model?