Fix getUiObject assertion

This was temporarily flipped to always fail while verifying changes to
DumpOnFailure, but was not flipped back in [1].

  [1]: I6dece3f39a2f3ee3273b6ef12e3314f807d3457f

Flag: EXEMPT testfix
Bug: 395783236
Test: atest InputMethodServiceTest#testBackButtonClick
Change-Id: Ifa2039950fcc52427a2bcbdd6800e2462a0be116