Update peaceiris/actions-gh-pages action to v4

Author: renovate[bot]

.github/workflows/doc.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Generate document
         run: gem install -N yard && yard doc
       - name: Publish Documentation on GitHub Pages
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./doc