Bump sphinx from 4.0.2 to 4.0.3 (#252)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 4.0.2 to 4.0.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v4.0.2...v4.0.3)

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