client audio: Fix flaky unit test

Fix for failing
LeAudioClientAudioTest#testLeAudioClientAudioSinkStartStop

Bug: 249099693
Test: atest BluetoothInstrumentationTests
Test: atest --host bluetooth_le_audio_test
Tag #feature

Merged-In: Ia1b22fd61253dc547fbafd536b42972727af4caf
Change-Id: Ia1b22fd61253dc547fbafd536b42972727af4caf
(cherry picked from commit 110dda3d)