Update dependency @next/mdx to v14

Author: renovate[bot]

package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@mdx-js/loader": "1.6.22",
-    "@next/mdx": "12.3.4",
+    "@next/mdx": "14.0.3",
     "next": "12.3.4",
     "react": "17.0.2",
     "react-dom": "17.0.2"