Add tests to validate no dangling destroyables

### 🐞 Describe the Bug
The master branch of `ember-lifeline` started failing its `canary` ember-try scenario with the following error:

https://github.com/ember-lifeline/ember-lifeline/runs/6181216496?check_suite_focus=true#step:6:116

Note the `(EventDispatcher)` string to identify the destroyable.

I'm unsure if it's related to:

https://github.com/emberjs/ember.js/commit/9fb35c41563d450293d991d313bd99f82b4acece

Which has the string `(EventDispatcher)` in its `toString`.

### 🔬 Minimal Reproduction
Run an addon with canary enabled.

### 😕 Actual Behavior
Dangling destroyables remain after tests are completed.

### 🤔 Expected Behavior
All destroyables are correctly destroyed (calling `assertDestroyablesDestroyed` passes).

### 🌍 Environment

- Ember: - 3.28.0
- Node.js/npm: - 12.22.1
- OS: - osx 12.2.1
- Browser: - Chrome 100

### ➕ Additional Context
N/A