Bump postcss from 8.5.19 to 8.5.21

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.19 to 8.5.21.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.19...8.5.21)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package.json

@@ -31,7 +31,7 @@
     "cross-env": "10.1.0",
     "css-loader": "7.1.4",
     "mini-css-extract-plugin": "2.10.2",
-    "postcss": "8.5.19",
+    "postcss": "8.5.21",
     "postcss-loader": "8.2.1",
     "postcss-scss": "4.0.9",
     "sass": "1.101.0",