improve: Updated Notebook learn\generation\langchain\handbook\05-langchain-retrieval-augmentation.ipynb (#476)

Now runs successfully and is up to date with latest LCEL methods.

## Problem

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why?

## Solution

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or other resources.

## Type of Change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [x] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

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Author: Siraj-Aizlewood