Prevent mockito initialization issue in ScreenshotViewModelTest

When this test runs first, we haven't yet done the check in waitUntilMockitoCanBeInitialized,
so for now, we need to run that first.  (This doesn't necessarily scale,
so hoping on a better solution for b/404544974 eventually)

Bug: 414420481
Test: ScreenshotViewModelTest
Flag: TEST_ONLY
Change-Id: I99fc2cfbd8644757c2d82f7a7575d94b309b65f1