avro

Bump rstest from 0.20.0 to 0.21.0 in /lang/rust (#2943)

Bumps [rstest](https://github.com/la10736/rstest) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/la10736/rstest/releases)
- [Changelog](https://github.com/la10736/rstest/blob/master/CHANGELOG.md)
- [Commits](https://github.com/la10736/rstest/compare/v0.20.0...v0.21.0)

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

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