Fix flaky unit test. (#3027)

.reuse/dep5

...oronawarnapp/test/debugoptions/ui/DebugOptionsFragment.kt

...app/test/debugoptions/ui/DebugOptionsFragmentViewModel.kt

...c/main/java/de/rki/coronawarnapp/util/ui/SmartLiveData.kt

.../src/test/java/testhelpers/extensions/LiveDataTestUtil.kt

...test/debugoptions/ui/DebugOptionsFragmentViewModelTest.kt