Bump postcss from 8.3.6 to 8.4.31 (#6697)

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.6 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@8.3.6...8.4.31)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -100,7 +100,7 @@
 		"node-zopfli-es": "1.0.7",
 		"nunjucks": "3.2.3",
 		"p-queue": "6.6.2",
-		"postcss": "8.3.6",
+		"postcss": "8.4.31",
 		"postcss-css-variables": "0.18.0",
 		"process": "0.11.10",
 		"randomstring": "1.2.1",