Update dependency postcss to v8.5.6

Author: renovate[bot]

package.json

@@ -34,7 +34,7 @@
     "eslint-plugin-prettier": "4.2.5",
     "eslint-plugin-solid": "0.14.5",
     "lefthook": "1.10.7",
-    "postcss": "8.5.1",
+    "postcss": "8.5.6",
     "prettier": "2.8.8",
     "prettier-plugin-astro": "0.14.1",
     "typescript": "5.7.3",