Update docs to point to assets-for-api-docs cupertino css file (#92932)

dev/docs/styles.html

@@ -4,7 +4,7 @@
 @import 'https://fonts.googleapis.com/css?family=Material+Icons|Material+Icons+Outlined|Material+Icons+Sharp|Material+Icons+Round';
 </style>
 
-<link href="https://flutter.github.io/cupertino_icons/css/icons.css" rel="stylesheet" type="text/css">
+<link href="https://flutter.github.io/assets-for-api-docs/assets/cupertino/cupertino.css" rel="stylesheet" type="text/css">
 
 <link href="../assets/overrides.css" rel="stylesheet" type="text/css">