Fix test flakiness

Flakiness noticed while running tests locally.

Test: atest services/tests/servicestests/src/com/android/server/timezonedetector/
Change-Id: I805bdf840f6b8c2ae6512b01fcb910af50478d2d

services/tests/servicestests/src/com/android/server/timezonedetector/TimeZoneDetectorServiceTest.java

@@ -190,6 +190,9 @@ public class TimeZoneDetectorServiceTest {
                     createTimeZoneConfiguration(true /* autoDetectionEnabled */);
             mTimeZoneDetectorService.updateConfiguration(autoDetectEnabledConfiguration);
 
+            // The configuration update notification is asynchronous.
+            mTestHandler.waitForMessagesToBeProcessed();
+
             verify(mMockContext).enforceCallingPermission(
                     eq(android.Manifest.permission.MANAGE_TIME_AND_ZONE_DETECTION),
                     anyString());