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 3.6.5 to 5.16.1
- [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@5.16.1/packages/astro)

Updates `@astrojs/mdx` from 1.1.5 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: astro
  dependency-version: 5.16.1
  dependency-type: direct:development
- dependency-name: "@astrojs/mdx"
  dependency-version: 4.3.12
  dependency-type: direct:development
...

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Author: dependabot[bot]