Bump peaceiris/actions-gh-pages from 3.8.0 to 3.9.0 (#3808)

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3.8.0 to 3.9.0.
- [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@068dc23...de7ea6f)

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

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/gh-pages.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Generate docs
         run: dart run tool/doc.dart --create-dirs --no-markdown --out lints --token ${{ secrets.GITHUB_TOKEN }}
       - name: Deploy docs
-        uses: peaceiris/actions-gh-pages@068dc23d9710f1ba62e86896f84735d869951305
+        uses: peaceiris/actions-gh-pages@de7ea6f8efb354206b205ef54722213d99067935
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_branch: gh-pages