docs: update sphinx theme

[sergiusens]

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run make lint?
• Have you successfully run pytest tests/unit?

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Replaces #4263

[codecov-commenter]

Codecov Report

Merging #4367 (9670947) into main (e340be1) will not change coverage.
The diff coverage is n/a.

❗ Current head 9670947 differs from pull request most recent head 72b136a. Consider uploading reports for the commit 72b136a to get more accurate results

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@@           Coverage Diff           @@
##             main    #4367   +/-   ##
=======================================
  Coverage   89.12%   89.12%           
=======================================
  Files         318      318           
  Lines       21171    21171           
=======================================
  Hits        18868    18868           
  Misses       2303     2303           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[lengau]

Looks good with the one suggested URL fix

[cmatsuoka]

Looks good, but there's a linting error to address.

[mr-cal]

tox run -e build-docs doesn't work for me on this branch, looks like CI is failing for a similar reason on tox run -e lint-docs

[sergiusens]

I mostly picked this up verbatim, @lengau would you know what's going on?

[lengau]

I think @mr-cal's PR #4375 got it :-)

[mr-cal]

Yep, that and 3 minor changes here. I think we're good to go.

• f3e238c
• 9670947
• d340902