Bump peaceiris/actions-gh-pages from 3 to 4

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3 to 4.
- [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...v4)

---
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/docsite.yml

@@ -39,7 +39,7 @@ jobs:
           name: site
           path: site
       - name: Publish
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           publish_branch: mkdocs
           publish_dir: site