Fix InputManager mocking in WindowMagnificationAnimationControllerTest

Once update_window_magnifier_bottom_boundary_with_mouse flag is enabled,
this test fails because of missing mock behavior.
This CL fixes it.

Bug: 419389153
Test: WindowMagnificationAnimationControllerTest
Flag: com.android.systemui.update_window_magnifier_bottom_boundary_with_mouse
Change-Id: I80dba84ef0d045a0027e3f65a43ba733e520204e