Fix one of the strict-zen-validation tests

Updating an existing AZR's CPS is always ignored, so the case we were trying to test never actually happened. Modified and renamed the test to verify the actual expected behavior (and made it non-flag dependent since the flag doesn't affect this particular part).

Bug: 420605963
Test: atest android.app.NotificationManagerZenTest
Flag: TEST_ONLY
Change-Id: Ie89248ada680611310c2405c0805b7f3c8dfc50d