WMLockScreenVisibilityMgrTest: update test for keyguard shell transit.

For this test, without transitions, we expect one call of each: 1)
ATMS#setLockscreenShown and ATMS#setKeyguardShown. But with shell
transitions, they are now both keyguardTransitions#startTransition.
Update test accordingly.

Bug: 364930619
Test: atest
Flag: com.android.window.flags.ensure_keyguard_does_transition_starting

Change-Id: Ia0907e0a2f6fc4832aa7a53b2b4c668012205103