chore(deps): bump @astrojs/mdx from 3.1.9 to 4.3.12

Bumps [@astrojs/mdx](https://github.com/withastro/astro/tree/HEAD/packages/integrations/mdx) from 3.1.9 to 4.3.12.
- [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@4.3.12/packages/integrations/mdx)

---
updated-dependencies:
- dependency-name: "@astrojs/mdx"
  dependency-version: 4.3.12
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]