bump postcss to 8.4.21

Author: mertasan

package.json

@@ -44,7 +44,7 @@
     "eslint-plugin-prettier": "^4.2.1",
     "fs-extra": "^10.0.0",
     "jest": "^29.4.3",
-    "postcss": "^8.4.16",
+    "postcss": "^8.4.21",
     "postcss-import": "^14.1.0",
     "prettier": "^2.5.0",
     "snapshot-diff": "^0.10.0",