chore(deps): bump astro from 5.15.3 to 5.16.4 in /manual

Bumps [astro](https://github.com/withastro/astro/tree/HEAD/packages/astro) from 5.15.3 to 5.16.4.
- [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@5.16.4/packages/astro)

---
updated-dependencies:
- dependency-name: astro
  dependency-version: 5.16.4
  dependency-type: direct:production
...

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Author: dependabot[bot]