use deno + setup-deno v2

https://github.com/denoland/setup-deno?tab=readme-ov-file#latest-stable-for-a-major

```yaml
- uses: denoland/setup-deno@v2
  with:
    deno-version: v2.x
```

Author: rdela

.github/workflows/build_demo.yml

@@ -18,9 +18,9 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Setup Deno environment
-        uses: denoland/setup-deno@v1
+        uses: denoland/setup-deno@v2
         with:
-          deno-version: v1.x
+          deno-version: v2.x
 
       - name: Build GitHub Pages with Lume
         uses: lumeland/build/gh-pages@main