🚀 Feature: Support Astro 6

[lishaduck]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Same as #940.

Additional Info

Blocking Flint from upgrading (not that we need to with any urgency)
Renovate PR: #1483

[JoshuaKGoldberg]

Yes please, this'd be very good!

[lishaduck]

Yes please, this'd be very good!

@cylewaitforit opened #1490 :)