Add `.astro` extension to the known extensions

[ematipico]

I want to request if you'd be open to the idea of adding .astro to the list of known file extensions

I know there was a previous (maybe different) request in the past: #149110

One of the reasons why I'd like to have native support as a known extension is because I would like to enable the Biome VS Code extension when an Astro file is open.