Deprecation warning violates `ember test --silent` behavior

According to the help for `ember test`:

```
--silent (Boolean) (Default: false) Suppress any output except for the test report
```

But the deprecation warning `DEPRECATION: Overriding init without calling this._super is deprecated. Please call this._super()` busts through that flag, breaking an automated CI workflow (because the CI output now includes these deprecation warnings instead of being only the test results).

Start by locating the implementation of `ember test --silent` and the code path that emits the deprecation warning. Reproduce the behavior with the command, then verify that the warning is suppressed while the test report remains available.

Written by the indexing model from the issue text.