Update dependency postcss to v8.4.21

Author: renovate[bot]

package.json

@@ -41,7 +41,7 @@
     "jest-environment-jsdom": "29.3.1",
     "jsdom": "20.0.3",
     "nuxt": "2.15.8",
-    "postcss": "8.4.20",
+    "postcss": "8.4.21",
     "prettier": "2.8.1",
     "tailwindcss": "3.2.4",
     "uid": "2.0.1",