Bump special windows layer adjustment

- Increase the special windows layer adjustment to account for windows boosted by an animation's
  z-ordering.

Bug: 63399929
Test: Launch PIP, launch Assistant, hit back and ensure that the dim
      layer draws under the PIP
Test: go/wm-smoke

Change-Id: I380db5b7a6b9fa707504251a48be139809afd96d