Update peaceiris/actions-gh-pages action to v4 (#6)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
         cat github-corner.html >> index.html
         sed -i "s/your-url/github.com\/${GH_USER}\/${REPO}/g" index.html
     - name: Deploy to GitHub Pages
-      uses: peaceiris/actions-gh-pages@v3
+      uses: peaceiris/actions-gh-pages@v4
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         publish_dir: .