ci: bump action upload-pages-artifact to v4

Author: NicolasCARPi

.github/workflows/push_demo.yml

@@ -47,7 +47,7 @@ jobs:
       - name: Setup Pages
         uses: actions/configure-pages@v3
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v4
         with:
           path: 'demo'
       - name: Deploy to GitHub Pages