Ignoring testOnScreenLock_cannotOpenMenu

The test inexplicably fails in presubmit/postsubmit,
but the failure cannot be reproduced locally. The test is low-impact,
so without a lead we've opted to set it to be ignored.

Test: atest AccessibilityMenuServiceTest
Bug: 324945360
Flag: N/A
Change-Id: I7bd819eb4cd1a914571a50e51c60ba002b333c22