ci(demo-deploy): migrate to GitHub Pages standard deployment workflow

Split the deploy job into build and deploy jobs, replacing
peaceiris/actions-gh-pages with the official
actions/upload-pages-artifact and actions/deploy-pages actions.
Add github-pages environment for deployment status tracking.

Author: orrisroot

.github/workflows/demo-deploy.yml

@@ -9,7 +9,7 @@ permissions:
   contents: write
 
 jobs:
-  deploy:
+  build:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -46,9 +46,18 @@ jobs:
       - name: Build demo
         run: npm run demo:build
 
-      - name: Deploy to GitHub Pages
-        uses: peaceiris/actions-gh-pages@v4
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./demo/dist
-          force_orphan: true
+          path: demo/dist
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4