Bump peaceiris/actions-gh-pages from 3.8.0 to 3.9.0

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@v3.8.0...v3.9.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Fixup docs
         run: find devel-docs/html/ -type f -name '*.html' -print0 | xargs -r -0 sed -i 's@/libenca/@/doc/@'
       - name: Deploy
-        uses: peaceiris/actions-gh-pages@v3.8.0
+        uses: peaceiris/actions-gh-pages@v3.9.0
         if: github.event_name == 'push' && github.event.ref == 'refs/heads/master'
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}