Bump postcss from 8.4.20 to 8.4.31 in /packages/modules/imodel-browser

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.20 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@8.4.20...8.4.31)

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

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

packages/modules/imodel-browser/package.json

@@ -63,7 +63,7 @@
     "jest-fetch-mock": "^3.0.3",
     "msw": "^0.27.1",
     "node-sass": "^6.0.0",
-    "postcss": "8.4.20",
+    "postcss": "8.4.31",
     "prettier": "^2.0.5",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",