message: Checkbox: Fix tests with sync'ed helper macro and associated fn
diff: @@ -27,7 +27,7 @@ pub use iced_style::checkbox::{Appearance, StyleSheet};
  ///
  /// let is_checked = true;
  ///
  -/// Checkbox::new(is_checked, "Toggle me!", Message::CheckboxToggled);
  +/// Checkbox::new("Toggle me!", is_checked, Message::CheckboxToggled);
  /// ```
  ///
  /// ![Checkbox drawn by `iced_wgpu`](https://github.com/iced-rs/iced/blob/7760618fb112074bc40b148944521f312152012a/docs/images/checkbox.png?raw=true)
  