Build(deps-dev): Bump postcss from 8.4.20 to 8.4.21 (#37851)

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:development
  update-type: version-update:semver-patch
...

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

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

package.json

@@ -140,7 +140,7 @@
     "lockfile-lint": "^4.10.0",
     "nodemon": "^2.0.20",
     "npm-run-all": "^4.1.5",
-    "postcss": "^8.4.20",
+    "postcss": "^8.4.21",
     "postcss-cli": "^10.1.0",
     "rollup": "^3.9.1",
     "rollup-plugin-istanbul": "^4.0.0",