Reduce (fix?) flakiness in dnd test

Provide time for an asynchronous call to finish

Test: this
Fixes: 149240922
Change-Id: I2eb4e6e64660850c96c65ec352b334b302f4f9d8
diff --git a/tests/app/src/android/app/cts/NotificationManagerTest.java b/tests/app/src/android/app/cts/NotificationManagerTest.java
index 0c4d6fe..459e01b 100644
--- a/tests/app/src/android/app/cts/NotificationManagerTest.java
+++ b/tests/app/src/android/app/cts/NotificationManagerTest.java
@@ -825,6 +825,8 @@
             mNotificationManager.setAutomaticZenRuleState(id1, onCondition1);
             mNotificationManager.setAutomaticZenRuleState(id2, onCondition2);
 
+            Thread.sleep(300); // wait for rules to be applied - it's done asynchronously
+
             mRuleIds.add(id1);
             mRuleIds.add(id2);
             assertExpectedDndState(INTERRUPTION_FILTER_PRIORITY);