build(deps): bump postcss from 8.4.20 to 8.4.21 (#1427)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.20 to 8.4.21.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.20...8.4.21)

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

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

package.json

@@ -79,7 +79,7 @@
         "monaco-themes": "^0.4.3",
         "mq-polyfill": "1.1.8",
         "navigator.locks": "^0.8.6",
-        "postcss": "^8.4.20",
+        "postcss": "^8.4.21",
         "postcss-flexbugs-fixes": "^5.0.2",
         "postcss-loader": "^7.0.2",
         "postcss-normalize": "^10.0.1",