reusables.actions.action-setup-python@v4, not @v3

[cclauss]

https://github.com/actions/setup-python/releases

reusables.actions.action-setup-python should be upgraded to setup-python@4, not @3.

Why:

See improvements and bug fixes at https://github.com/actions/setup-python/releases

What's being changed:

Check off the following:

• I have reviewed my changes in staging (look for "Automatically generated comment" and click Modified to view your latest changes).
• For content changes, I have completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[janiceilene]

@cclauss Thanks so much for opening a PR! I'll get this triaged for review ✨

In the meantime, can you add some information to the Why section of the OP ☝️ to explain why this change should be made in the docs?

[skedwards88]

Thanks for this update! We'll get this merged down for you.

[github-actions]

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