chore: bump vite-plugin-svelte to 4.0.0-next in demo and preview site (#12385)

Author: dominikg

playgrounds/demo/package.json

@@ -12,7 +12,7 @@
     "preview": "vite preview"
   },
   "devDependencies": {
-    "@sveltejs/vite-plugin-svelte": "^3.1.0",
+    "@sveltejs/vite-plugin-svelte": "^4.0.0-next.3",
     "nodemon": "^3.0.3",
     "polka": "^1.0.0-next.25",
     "svelte": "workspace:*",