Add missing @Test annotation to ignoresGesture_transitionInProgress

This change is intentionally a no-op on master because the tag already
exists on master.

Test: m -j
Test: atest BackAnimationControllerTest#ignoresGesture_transitionInProgress
Bug: 232793611

Change-Id: I1738b40c8df1c9af7bb0e63586cb2e70b3c9e8ca