Bump postcss-mixins from 9.0.3 to 9.0.4

Bumps [postcss-mixins](https://github.com/postcss/postcss-mixins) from 9.0.3 to 9.0.4.
- [Release notes](https://github.com/postcss/postcss-mixins/releases)
- [Changelog](https://github.com/postcss/postcss-mixins/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss-mixins@9.0.3...9.0.4)

---
updated-dependencies:
- dependency-name: postcss-mixins
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -34,7 +34,7 @@
     "postcss-custom-properties": "^12.1.8",
     "postcss-hash": "^3.0.0",
     "postcss-import": "^14.1.0",
-    "postcss-mixins": "^9.0.3",
+    "postcss-mixins": "^9.0.4",
     "postcss-nested": "^5.0.6",
     "postcss-nesting": "^10.1.10",
     "postcss-scss": "^4.0.4",