Bump pallets-sphinx-themes from 2.0.3 to 2.1.0

Bumps [pallets-sphinx-themes](https://github.com/pallets/pallets-sphinx-themes) from 2.0.3 to 2.1.0.
- [Release notes](https://github.com/pallets/pallets-sphinx-themes/releases)
- [Changelog](https://github.com/pallets/pallets-sphinx-themes/blob/main/CHANGES.rst)
- [Commits](https://github.com/pallets/pallets-sphinx-themes/compare/2.0.3...2.1.0

)

---
updated-dependencies:
- dependency-name: pallets-sphinx-themes
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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