Fixed "this.args is undefined" error when pressing Escape to close roles modal

no issue

- the modal component is using a native class but with the `@classic` decorator so it's still using pre-Glimmer component syntax where `this.args` doesn't exist
- fixes Sentry error `ADMIN-4C`

ghost/admin/app/components/modal-select-user-role.js

@@ -33,7 +33,7 @@ export default class ModalPostPreviewComponent extends ModalBase {
 
         // needed because ModalBase uses .send() for keyboard events
         closeModal() {
-            this.args.close();
+            this.close();
         }
     }
 }