Ensure UpdateNotificationThread being terminated

There are cases where the NotificationUpdateThread
continues running after a test finishes.
This can interfere with susequent tests and
potentially cause failures.

Ensure the thread is terminated to prevent these issuse.

Flag: EXEMPT, test change
Bug: 369936658
Test: atest BluetoothOppServiceCleanupTest BluetoothOppServiceTest
--iterations 100

Change-Id: Iaddd50df409c335019213de3b21d741808e4d2ec