chore: icon alias improvements (#2861)

Co-authored-by: Eric Fennis <eric.fennis@gmail.com>

tools/build-icons/utils/deprecationReasonTemplate.ts

@@ -28,6 +28,6 @@ export default function deprecationReasonTemplate(
     case 'icon.brand':
       return `Brand icons have been deprecated and are due to be removed, please refer to https://github.com/lucide-icons/lucide/issues/670. We recommend using https://simpleicons.org/?q=${iconName} instead.${removalNotice}`;
     default:
-      return '';
+      throw new Error(`Unknown deprecation reason: ${deprecationReason}`);
   }
 }