Fix AudioPlaybackConfigurationTests with stream muted

This is just a workaround until we fix the reporting of multiple muting
sources.

Test: notification stream mute + atest AudioPlaybackConfigurationTests
Bug: 319062503
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c389590b7c78b889366d98edea6e239f2b54d2e1)
Merged-In: I29ac34e00a0f810b53f40cb4ce743942d511e363
Change-Id: I29ac34e00a0f810b53f40cb4ce743942d511e363