Fix minimization related flicker tests

The expected behavior was changed by b/421124396 to show the wallpaper
after minimizing the last task.
This CL updates the test expectation.

Bug: 431505919
Test: atest WMShellFlickerTestsDesktopMode:com.android.wm.shell.flicker.MinimizeAppsLandscape
Flag: EXEMPT test only change
Change-Id: I242cdd6439c926506ba487d1ae89c3f3a50cd2e6