Composing validations stopped working in Ember 3.10

### Environment

- Ember Version: 3.10
- Ember CLI Version: 3.8.0
- Ember CP Validations Version: 4.0.0-beta.9

### Steps to Reproduce

Before I updated to ember-source 3.10 (and to make it work, ember-cp-validations 4.0.0-beta.9), we had code like this that worked fine:

```js
const Validations = buildValidations(
{
...
}
);

export const SharedValidations = buildValidations(
{
...
}
);

export default Model.extend(Validations, SharedValidations, { });
```

After upgrading, this stopped working. I ended up just manually merging the validations and repeating the declarations, but wanted to let you know that this happened - it's also not really well documented, so not sure if that was even _supposed_ to work (although it was a quite handy feature...!).