Update peaceiris/actions-gh-pages action to v4

Author: renovate[bot]

.github/workflows/cd.yml

@@ -29,7 +29,7 @@ jobs:
           name: Website
 
       - 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: ./