[Thread] fix wrong kotlin argument name

Fixes build warning:
```
the corresponding parameter in the supertype 'LifecycleEventObserver' is named 'source'. This may cause problems when calling this function with named arguments.
    override fun onStateChanged(lifecycleOwner: LifecycleOwner, event: Lifecycle.Event) {
```

Bug: 327098435
Change-Id: I9c50ab508cd39bf2eda02c423deeef9ca5342f4f