Bump furo from 2022.6.4.1 to 2022.6.21 in /docs (#3138)

Bumps [furo](https://github.com/pradyunsg/furo) from 2022.6.4.1 to 2022.6.21.
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](https://github.com/pradyunsg/furo/compare/2022.06.04.1...2022.06.21

)

---
updated-dependencies:
- dependency-name: furo
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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