chore(deps-dev): bump astro and @astrojs/mdx

Bumps [astro](https://github.com/withastro/astro/tree/HEAD/packages/astro) and [@astrojs/mdx](https://github.com/withastro/astro/tree/HEAD/packages/integrations/mdx). These dependencies needed to be updated together.

Updates `astro` from 5.18.1 to 6.1.2
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/astro/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/astro@6.1.2/packages/astro)

Updates `@astrojs/mdx` from 4.3.14 to 5.0.3
- [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/mdx@5.0.3/packages/integrations/mdx)

---
updated-dependencies:
- dependency-name: astro
  dependency-version: 6.1.2
  dependency-type: direct:development
  update-type: version-update:semver-major
- dependency-name: "@astrojs/mdx"
  dependency-version: 5.0.3
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -22,7 +22,7 @@
   },
   "devDependencies": {
     "@astrojs/check": "0.9.8",
-    "@astrojs/mdx": "4.3.14",
+    "@astrojs/mdx": "5.0.3",
     "@astrojs/react": "4.3.1",
     "@astrojs/sitemap": "3.7.2",
     "@axe-core/playwright": "4.11.1",
@@ -42,7 +42,7 @@
     "@playwright/test": "1.58.2",
     "@types/react": "19.2.14",
     "@typescript-eslint/parser": "8.57.2",
-    "astro": "5.18.1",
+    "astro": "6.1.2",
     "eslint": "10.1.0",
     "eslint-plugin-astro": "1.6.0",
     "prettier": "3.8.1",