AFAICT `asset.attrs` is a shallow object and does not implement the [`Copyable` interface][1]
or the `copy` method. Calling the `copy` function from ember-copy on it therefore only
creates a shallow copy.

This is exactly what [`assign`][2] does, when you assign into an empty object.

Referencing evoactivity#77.

[1]: https://www.emberjs.com/api/ember/release/classes/Ember.Copyable
[2]: https://emberjs.com/api/api/ember/release/functions/@ember%2Fpolyfills/assign