Use @boolean for true and false in highlights (#25338)

Release Notes:

- Fixed issue where `true` and `false` were highlighted as constants,
ignoring the `boolean` highlight defined in themes.
  - This fix applies to: C, C++, Go, JSON, JSONC, Python, and Rust.

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/languages/src/json/highlights.scm

@@ -11,6 +11,9 @@
 [
   (true)
   (false)
+] @boolean
+
+[
   (null)
 ] @constant