Test not waiting promises

### Problem

The test is not waiting the promise to return the data.
Ember version: 3.4

### Test scenario

I'm using `triggerKeyEvent` to trigger an action at a text input:
```js
await fillIn('[data-test-search-input]', 'Test');
await triggerKeyEvent('[data-test-search-input]', 'keydown', 13);
await settled();
```
The action goes on a server and gets some data:
```js
actions: {
onTriggerKey() {
return this.getDataFromServer().then(data => set(this, 'data', data));
}
}
```
But i'm facing some strange behaviours. Sometimes the `await settled()` wait the promise return the data and sometimes not. This is very hard to reproduce because the test pass in the most of the times.