Update dependency postcss to ^8.5.6

Author: renovate[bot]

package.json

@@ -41,7 +41,7 @@
     "@types/react-dom": "^19.0.3",
     "autoprefixer": "^10.4.20",
     "eslint": "^9.20.1",
-    "postcss": "^8.5.2",
+    "postcss": "^8.5.6",
     "prettier": "^3.5.1",
     "tailwindcss": "^3.4.17",
     "turbo": "^2.4.2",