Bump postcss from 8.5.3 to 8.5.6

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.3 to 8.5.6.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.3...8.5.6)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.6
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "archiver": "^7.0.1",
     "autoprefixer": "^10.4.21",
     "cssnano": "^7.0.6",
-    "postcss": "^8.5.3",
+    "postcss": "^8.5.6",
     "postcss-cli": "^11.0.1",
     "postcss-custom-media": "^11.0.5",
     "postcss-custom-selectors": "^8.0.4",