minor update: pathfinder notebook

[aphc14]

Description

Updates pathfinder notebook to use the Pathfinder implementation since pymc-extras>=0.2.2 to better compare Pathfinder's performance compared to NUTS sampling for the eight schools dataset.

Note: This is just an interim update to the notebook while a more detailed notebook, tutorial and case-study of Pathfinder is underway!

resolves #572

Checklist

• Notebook follows style guide https://docs.pymc.io/en/latest/contributing/jupyter_style.html
• PR description contains a link to the relevant issue:
  • a tracker one for existing notebooks (tracker issues have the "tracker id" label)
  • or a proposal one for new notebooks
• Check the notebook is not excluded from any pre-commit check: https://github.com/pymc-devs/pymc-examples/blob/main/.pre-commit-config.yaml

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📚 Documentation preview 📚: https://pymc-examples--774.org.readthedocs.build/en/774/

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[fonnesbeck]

LGTM