Bump @tailwindcss/postcss from 4.0.0-beta.6 to 4.0.0-beta.8

Bumps [@tailwindcss/postcss](https://github.com/tailwindlabs/tailwindcss/tree/HEAD/packages/@tailwindcss-postcss) from 4.0.0-beta.6 to 4.0.0-beta.8.
- [Release notes](https://github.com/tailwindlabs/tailwindcss/releases)
- [Changelog](https://github.com/tailwindlabs/tailwindcss/blob/next/CHANGELOG.md)
- [Commits](https://github.com/tailwindlabs/tailwindcss/commits/v4.0.0-beta.8/packages/@tailwindcss-postcss)

---
updated-dependencies:
- dependency-name: "@tailwindcss/postcss"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -21,7 +21,7 @@
   "devDependencies": {
     "@rsbuild/core": "^1.1.13",
     "@rsbuild/plugin-svelte": "^1.0.7",
-    "@tailwindcss/postcss": "4.0.0-beta.6",
+    "@tailwindcss/postcss": "4.0.0-beta.8",
     "prettier": "^3.4.2",
     "prettier-plugin-svelte": "^3.3.2",
     "prettier-plugin-tailwindcss": "^0.6.9",