Bump peaceiris/actions-gh-pages from 3.7.3 to 3.9.3 (#53)

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3.7.3 to 3.9.3.
- [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@v3.7.3...v3.9.3)

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

.github/workflows/docs.yml

@@ -17,7 +17,7 @@ jobs:
           poetry-version: "1.1.13"
       - run: poetry install --extras all
       - run: poetry run mkdocs build
-      - uses: peaceiris/actions-gh-pages@v3.7.3
+      - uses: peaceiris/actions-gh-pages@v3.9.3
         with:
           github_token: "${{ secrets.GITHUB_TOKEN }}"
           publish_dir: ./site