Bump postcss from 8.2.13 to 8.4.31 in /packages/optimizer

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.13 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@8.2.13...8.4.31)

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

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

packages/optimizer/package.json

@@ -45,7 +45,7 @@
     "https-proxy-agent": "5.0.0",
     "lru-cache": "6.0.0",
     "normalize-html-whitespace": "1.0.0",
-    "postcss": "8.2.13",
+    "postcss": "8.4.31",
     "postcss-safe-parser": "5.0.2",
     "terser": "5.5.1"
   },