Fix exception for getActiveSubscriptionInfo() in CellBroadcastReceiverOemUnitTests

Mocking for getActiveSubscriptionInfo() of SubscriptionManager should be added

Bug: 369737253
Test: atest com.android.cellbroadcastreceiver.unit.CellBroadcastAlertSettingsTest
Flag: TEST_ONLY
Change-Id: I20d938ce47fbc49b563d1bf0e1e10c4fc81d9032
1 file changed