Bump dartdoc from 8.0.7 to 8.0.8 (#2300)

Bumps [dartdoc](https://github.com/dart-lang/dartdoc) from 8.0.7 to 8.0.8.
- [Release notes](https://github.com/dart-lang/dartdoc/releases)
- [Changelog](https://github.com/dart-lang/dartdoc/blob/main/CHANGELOG.md)
- [Commits](https://github.com/dart-lang/dartdoc/commits)

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

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