Update dependency @astrojs/mdx to v4

| datasource | package      | from  | to    |
| ---------- | ------------ | ----- | ----- |
| npm        | @astrojs/mdx | 3.1.7 | 4.3.4 |

Author: renovate[bot]

package.json

@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/check": "^0.9.3",
-    "@astrojs/mdx": "^3.1.7",
+    "@astrojs/mdx": "^4.0.0",
     "@astrojs/rss": "^4.0.7",
     "@astrojs/sitemap": "^3.2.0",
     "@fontsource/roboto-mono": "^5.1.0",