Update dependency @astrojs/mdx to v5

Author: renovate[bot]

package.json

@@ -11,7 +11,7 @@
     },
     "dependencies": {
         "@astrojs/check": "0.9.8",
-        "@astrojs/mdx": "4.3.14",
+        "@astrojs/mdx": "5.0.3",
         "@astrojs/rss": "4.0.17",
         "@astrojs/sitemap": "3.7.1",
         "astro": "5.18.1",