navigatesToListAndBack_portrait flaky on api 21

[rjrjr]

Getting to be like 50/50.

com.squareup.sample.mainactivity.TodoAppTest > navigatesToListAndBack_portrait[test(AVD) - 5.0.2] FAILED 
	java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.activity.OnBackPressedDispatcher.addCallback(androidx.lifecycle.LifecycleOwner, androidx.activity.OnBackPressedCallback)' on a null object reference
	at com.squareup.workflow1.ui.HandleBackPressWhenAttached.onViewAttachedToWindow(BackPressHandler.kt:77)
Tests on test(AVD) - 5.0.2 failed: Instrumentation run failed due to 'java.lang.NullPointerException'