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
  update-type: version-update:semver-patch
...

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

package.json

@@ -80,7 +80,7 @@
     "lockfile-lint": "^4.12.1",
     "npm-run-all2": "^6.0.6",
     "picocolors": "^1.0.0",
-    "postcss": "^8.4.29",
+    "postcss": "^8.4.31",
     "postcss-cli": "^10.1.0",
     "stylelint": "^15.10.3",
     "stylelint-config-twbs-bootstrap": "^11.0.1",