Bump postcss from 8.2.13 to 8.2.15 (#33931)

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.13 to 8.2.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.2.13...8.2.15)

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

package.json

@@ -136,7 +136,7 @@
     "lockfile-lint": "^4.6.2",
     "nodemon": "^2.0.7",
     "npm-run-all": "^4.1.5",
-    "postcss": "^8.2.13",
+    "postcss": "^8.2.15",
     "postcss-cli": "^8.3.1",
     "rollup": "^2.47.0",
     "rollup-plugin-istanbul": "^3.0.0",