Update pages action to v4

Author: rbuckton

.github/workflows/pr.yml

@@ -12,7 +12,7 @@ jobs:
       - run: npm install
       - run: npm run build
       - name: Publish HTML to GitHub Pages
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           publish_dir: ./build
           destination_dir: pr/${{ github.event.number }}/