Update dependency next to v16

Author: renovate[bot]

sandbox-templates/mdx-loader-next/package.json

@@ -1,7 +1,7 @@
 {
   "dependencies": {
     "@mdx-js/loader": "^3.0.0",
-    "next": "^15.0.0",
+    "next": "^16.0.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0"
   },