Helper "not" has wrong value when passing PromiseProxy

[nag5000]

This bug actually related to all truthConvert-helpers.
Initially, I reproduced this bug with an ember-data model (async belongsTo relationship), but it can be reproduced on any Ember.ProxyMixin based object.

What's going on here:

1. I have an ember-data model in loading state (isPending == true)
2. {{not model}} returns true (offtopic: isn't that weird already? model != null, so I expect false as result of {{not model}}). OK, it returns true because truthConvert checks isTruthy and model.isTruthy === false until it is fulfilled.
3. After some time, the model is loaded. model.isTruthy becomes true, model.isSettled === true.
4. {{not model}} is not recomputed, it still returns true (expected false).

Ember: 3.4.8
Ember Data: 3.4.4
ember-truth-helpers: 2.1.0

Demo: https://ember-twiddle.com/1dd51cbbc7e12f94e255913ef279baec?openFiles=controllers.application.js%2C