Fix nullable type

Corona-Warn-App/src/androidTest/java/testhelpers/TestApplication.kt

@@ -46,7 +46,7 @@ class TestApplication : Application(), HasAndroidInjector {
 
             override fun onActivityStopped(activity: Activity) = Unit
 
-            override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle?) = Unit
+            override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) = Unit
 
             override fun onActivityDestroyed(activity: Activity) = Unit
         })