Deflake BubbleBarViewAnimatorTest

Fix an issue where we were verifying the status of the animator on the
test thread, which may have been modified on the main thread.

100x runs: https://android-build.corp.google.com/abtd/run/L42700030003806035/

Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DEVELOPMENT
Fixes: 339437686
Test: abtd link above
Change-Id: I7e0d67e6ca4b2f905ff80f317355d8d5ed0a912b