Bump peaceiris/actions-gh-pages from 3.9.1 to 4.0.0

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3.9.1 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@64b46b4...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/docs.yml

@@ -46,7 +46,7 @@ jobs:
         if: github.event_name == 'push' && github.actor != 'dependabot[bot]'
         # We pin to the SHA, not the tag, for security reasons.
         # https://docs.github.com/en/actions/learn-github-actions/security-hardening-for-github-actions#using-third-party-actions
-        uses: peaceiris/actions-gh-pages@64b46b4226a4a12da2239ba3ea5aa73e3163c75b # v3.9.1
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e # v4.0.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: .github/pages