ci: bump peaceiris/actions-gh-pages from v3 to v3.8.0 (#194)

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from v3 to v3.8.0.
- [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...068dc23)

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

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

.github/workflows/gh-pages.yml

@@ -42,7 +42,7 @@ jobs:
 
       - name: Deploy to GitHub Pages
         if: github.ref == 'refs/heads/master'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v3.8.0
         with:
           deploy_key: ${{ secrets.ACTIONS_DEPLOY_KEY }}
           publish_dir: ./site