Disable certain test cases for PiP2

In PiP2, after the call to enterPictureInPictureMode, WM Shell does not
immediately signal the core to trigger onTaskAppeared.

Flag: com.android.wm.shell.enable_pip2
Bug: 378549723
Test: atest WindowOrganizerTests
Change-Id: Ia7817fc8991f826545b80847861fa04514e9caa4