Bump postcss from 7.0.36 to 8.4.31 in /node-bb/install (#12014)

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.36 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@7.0.36...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>

node-bb/install/package.json

@@ -113,7 +113,7 @@
     "passport-local": "1.0.0",
     "pg": "^8.0.2",
     "pg-cursor": "^2.1.9",
-    "postcss": "7.0.36",
+    "postcss": "8.4.31",
     "postcss-clean": "1.1.0",
     "promise-polyfill": "^8.1.3",
     "prompt": "^1.0.0",