Update Astro (and related packages)

[coliff]

Closes #42436

Description

Right now, if you run npm run start or npm run docs then the site will be available in the browser but any changes made in examples will not update in the browser (even with force refresh).

Motivation & Context

This was caused by an upstream bug in Astro, which was resolved for 6.3.7.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-42437--twbs-bootstrap.netlify.app/

Related issues

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates Astro framework and related dev tooling versions in package.json to pick up newer fixes/features.

Changes:

• Bump astro from ^6.1.8 to ^6.3.7
• Bump @astrojs/check, @astrojs/markdown-remark, and @astrojs/mdx to newer patch versions

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[julien-deramond]

Thanks. I'll review this while I update the v5 and v6 deps. I was off for a couple of weeks, but I'll be back to it soon :) Since it's annoying, I'll try to do it tonight for this part.

[julien-deramond]

Thanks for bringing #42436 to everyone's attention. Tested locally to live update one of the examples, and it works well, so LGTM.