Bump @astrojs/starlight from 0.38.4 to 0.39.3

Bumps [@astrojs/starlight](https://github.com/withastro/starlight/tree/HEAD/packages/starlight) from 0.38.4 to 0.39.3.
- [Release notes](https://github.com/withastro/starlight/releases)
- [Changelog](https://github.com/withastro/starlight/blob/main/packages/starlight/CHANGELOG.md)
- [Commits](https://github.com/withastro/starlight/commits/@astrojs/starlight@0.39.3/packages/starlight)

---
updated-dependencies:
- dependency-name: "@astrojs/starlight"
  dependency-version: 0.39.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]