Bump postcss from 8.4.16 to 8.4.20

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.16 to 8.4.20.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.16...8.4.20)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package.json

@@ -83,7 +83,7 @@
         "optimize-css-assets-webpack-plugin": "^6.0.1",
         "os-browserify": "^0.3.0",
         "pnp-webpack-plugin": "^1.6.4",
-        "postcss": "8.4.16",
+        "postcss": "8.4.20",
         "postcss-flexbugs-fixes": "^5.0.2",
         "postcss-loader": "^7.0.1",
         "postcss-normalize": "^10.0.0",