Bump peaceiris/actions-mdbook from 1.2.0 to 2.0.0

Bumps [peaceiris/actions-mdbook](https://github.com/peaceiris/actions-mdbook) from 1.2.0 to 2.0.0.
- [Release notes](https://github.com/peaceiris/actions-mdbook/releases)
- [Changelog](https://github.com/peaceiris/actions-mdbook/blob/main/CHANGELOG.md)
- [Commits](https://github.com/peaceiris/actions-mdbook/compare/adeb05db28a0c0004681db83893d56c0388ea9ea...ee69d230fe19748b7abf22df32acaa93833fad08

)

---
updated-dependencies:
- dependency-name: peaceiris/actions-mdbook
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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