chore(deps): update dependency @astrojs/mdx to v4

Author: renovate[bot]

package.json

@@ -18,7 +18,7 @@
   "devDependencies": {
     "@astrojs/check": "^0.9.4",
     "@astrojs/markdown-remark": "^6.0.1",
-    "@astrojs/mdx": "^3.1.9",
+    "@astrojs/mdx": "^4.0.0",
     "@astrojs/sitemap": "^3.2.1",
     "@astrolib/seo": "1.0.0-beta.8",
     "@vitest/coverage-v8": "3.1.1",