Bump typing-extensions from 4.1.1 to 4.2.0 (#389)

Bumps [typing-extensions](https://github.com/python/typing) from 4.1.1 to 4.2.0.
- [Release notes](https://github.com/python/typing/releases)
- [Changelog](https://github.com/python/typing/blob/master/typing_extensions/CHANGELOG)
- [Commits](python/typing@4.1.1...4.2.0)

---
updated-dependencies:
- dependency-name: typing-extensions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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