Bump the known_good_semver group with 1 update (#1375)

Bumps the known_good_semver group with 1 update: [syn](https://github.com/dtolnay/syn).

- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](https://github.com/dtolnay/syn/compare/2.0.29...2.0.31)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: known_good_semver
...

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