bevy::main_return_without_appexit is emitted when AppExit is stored in a variable

[BD103]

fn main() {
    let app_exit = App::new().run();
    println!("{app_exit:?}");
}

The above causes a warning, though it probably shouldn't. While the intended solution is to return AppExit, there are multiple others. We mainly just want AppExit to be handled, so Apps do not silently fail.