build(deps-dev): bump postcss from 8.4.29 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.29 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.29...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

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

package.json

@@ -42,7 +42,7 @@
         "laravel-mix": "^6.0.49",
         "laravel-mix-purgecss": "^6.0.0",
         "popper.js": "^1.16.1",
-        "postcss": "^8.4.19",
+        "postcss": "^8.4.31",
         "resolve-url-loader": "^5.0.0",
         "sass": "^1.56.1",
         "sass-loader": "^13.2.0",