Car: Fix assertThat in CarSetupWizardLayoutTest

Truth.assertThat is a fluent-style API. Fix the tests to actually
do something.

Found by errorprone.

Bug: 73513670
Test: m RunCarSetupWizardLibRoboTests
Test: m javac-check RUN_ERROR_PRONE=true
Change-Id: I6043ed910fda0569aa27174fa7cc61c19eeb2229