Fix ci build error

Author: bugsweeper

examples/app/headless_renderer.rs

@@ -491,7 +491,7 @@ mod frame_capture {
                             };
                         }
                         if scene_controller.single_image {
-                            app_exit_writer.send(AppExit);
+                            app_exit_writer.send(AppExit::Success);
                             break;
                         }
                     }