Bump postcss-custom-properties from 12.1.9 to 14.0.4

Bumps [postcss-custom-properties](https://github.com/csstools/postcss-plugins/tree/HEAD/plugins/postcss-custom-properties) from 12.1.9 to 14.0.4.
- [Changelog](https://github.com/csstools/postcss-plugins/blob/main/plugins/postcss-custom-properties/CHANGELOG.md)
- [Commits](https://github.com/csstools/postcss-plugins/commits/HEAD/plugins/postcss-custom-properties)

---
updated-dependencies:
- dependency-name: postcss-custom-properties
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

package.json

@@ -98,7 +98,7 @@
     "json-loader": "^0.5.7",
     "postcss": "^8.4.25",
     "postcss-cli": "^9.1.0",
-    "postcss-custom-properties": "^12.1.9",
+    "postcss-custom-properties": "^14.0.4",
     "postcss-custom-selectors": "^6.0.3",
     "postcss-load-plugins": "^2.3.0",
     "postcss-loader": "^4.1.0",