Bump peaceiris/actions-gh-pages from 3.7.3 to 4.0.0

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3.7.3 to 4.0.0.
- [Release notes](https://github.com/peaceiris/actions-gh-pages/releases)
- [Changelog](https://github.com/peaceiris/actions-gh-pages/blob/main/CHANGELOG.md)
- [Commits](peaceiris/actions-gh-pages@bbdfb20...4f9cc66)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/build.yml

@@ -49,7 +49,7 @@ jobs:
       - name: Push to gh-pages
         if: success() && github.event_name == 'push'
         # Don't use tags: https://julienrenaux.fr/2019/12/20/github-actions-security-risk/
-        uses: peaceiris/actions-gh-pages@bbdfb200618d235585ad98e965f4aafc39b4c501
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./output