If you implement custom actions in Herald, you should now subclass `HeraldAction` instead of `HeraldCustomAction`.
The `HeraldCustomAction` class no longer exists, and code extending it will not load, work, or have any effect.
The API for `HeraldAction` differs from the API for `HeraldCustomAction`. You can look at the native actions (which now also extend `HeraldAction`) for guidance.
See T8726 for some context.