Update dependency postcss to v8.5.6 (#534)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -42,7 +42,7 @@
     "eslint": "9.29.0",
     "eslint-config-stylelint": "23.0.0",
     "npm-run-all2": "7.0.2",
-    "postcss": "8.5.5",
+    "postcss": "8.5.6",
     "prettier": "3.5.3",
     "remark-cli": "12.0.1",
     "stylelint": "16.20.0"