Bump postcss from 8.3.8 to 8.3.9 (#35110)

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.8 to 8.3.9.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.3.8...8.3.9)

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

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

Author: dependabot[bot]

package-lock.json

@@ -138,7 +138,7 @@
     "lockfile-lint": "^4.6.2",
     "nodemon": "^2.0.13",
     "npm-run-all": "^4.1.5",
-    "postcss": "^8.3.8",
+    "postcss": "^8.3.9",
     "postcss-cli": "^9.0.1",
     "rollup": "^2.58.0",
     "rollup-plugin-istanbul": "^3.0.0",