chore(deps): update peaceiris/actions-gh-pages action to v4

Author: renovate[bot]

.github/workflows/docs.yml

@@ -21,7 +21,7 @@ jobs:
         run: cargo doc --no-deps --document-private-items
 
       - name: Publish to GitHub pages
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./target/doc