leaudio: Fix yet another alarm cancel missing.

Fixes the race which could lead to link drop on timeout which should be
canceled.
This patch also adds unit test update which verifies alarm canceling
behaviour.

Bug: 255291874
Test: atest bluetooth_le_audio_test
Test: atest BluetoothInstrumentationTests
Test: Manual testing
Tag: #feature

Merged-In: I213b3e39e1f9e30187cd7313069d0fbf06bc34bc
Change-Id: I213b3e39e1f9e30187cd7313069d0fbf06bc34bc
(cherry picked from commit 57c09df7)