astro: Fix Tailwind LS not working in attributes (zed-industries#12741)

This fixes zed-industries#12402.

We already had the `tailwind-language-server` config in Astro's
`config.toml` here:
https://github.com/zed-industries/zed/blob/fd39f20842967f0fb8a6c508bc2e1ebaefbaf15f/extensions/astro/languages/astro/config.toml#L17-L23

But it's not enough to add `overrides.string` to the `config.toml`, you
also need an `overrides.scm` file that sets the overrides.

And, tricky bit, when you add a single override to the `overrides.scm`
file you have to add all of them that Zed knows about. In my case, I had
to add `@comment` too, because Zed somehow expects that.

Release Notes:

- Fixed `tailwind-language-server` not working in attributes inside of
`*.astro` files.
([zed-industries#12402](zed-industries#12402)).

Demo/proof:


https://github.com/zed-industries/zed/assets/1185253/05677a2d-831d-4e05-a1a2-4d1730ce2a46

extensions/astro/languages/astro/overrides.scm

@@ -0,0 +1,6 @@
+[
+  (attribute_value)
+  (quoted_attribute_value)
+] @string
+
+(comment) @comment