CI: (deps): 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/docs.yml

@@ -81,7 +81,7 @@ jobs:
       run: echo "DOC_VERSION=v${{ needs.Docs.outputs.doc-version }}" >> $GITHUB_ENV
 
     - name: Upload to GitHub Pages
-      uses: peaceiris/actions-gh-pages@v3
+      uses: peaceiris/actions-gh-pages@v4
       with:
         deploy_key: ${{ secrets.GHPAGES_DEPLOY_KEY }}
         publish_dir: ./docs/build/html