Fixing TaplTestsQuickstep#testQuickSwitchToPreviousAppForTablet()

Currently, test asssumes that we are in persistent taskbar mode and assumes that taskbar is visible after switching to non ime activity.

We need overall strategy to how we migrate currentl TaplTestQuickstep to test for transient taskbar mode also. But, this will fix the current flakiness.

Test: Pre-submit
Flag: not needed
Bug: 281772186
Change-Id: Ie7e3364febd38ce489c3d3c881b94b8b308d3cb5