Check events for launching split from Launchable

* Previously we weren't waiting for any events check,
which was terminating the test too early before any
split cleanup was happening, causing errors in the
following test.

Test: atest NexusLauncherOutOfProcTests:com.android.quickstep.TaplTestsSplitscreen
Bug: 297135374
Change-Id: I635a1de1381932e6545fc0fc7bf7567c9f6ebe67