Bump @astrojs/mdx from 3.1.8 to 3.1.9 (#24)

Bumps [@astrojs/mdx](https://github.com/withastro/astro/tree/HEAD/packages/integrations/mdx) from 3.1.8 to 3.1.9.
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/integrations/mdx/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/@astrojs/[email protected]/packages/integrations/mdx)

---
updated-dependencies:
- dependency-name: "@astrojs/mdx"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -11,7 +11,7 @@
     "deploy": "astro build && firebase deploy"
   },
   "dependencies": {
-    "@astrojs/mdx": "^3.1.8",
+    "@astrojs/mdx": "^3.1.9",
     "@astrojs/rss": "^4.0.9",
     "@astrojs/sitemap": "^3.2.1",
     "astro": "^4.16.8",