Return mocked AudioManager in car unit tests

Bug: 110532739
Test: atest CarServiceTest
Change-Id: I12d8499e5b3cca6696b934b03d89647a271113c0
diff --git a/tests/carservice_test/src/com/android/car/MockedCarTestBase.java b/tests/carservice_test/src/com/android/car/MockedCarTestBase.java
index a57d800..3a50b45 100644
--- a/tests/carservice_test/src/com/android/car/MockedCarTestBase.java
+++ b/tests/carservice_test/src/com/android/car/MockedCarTestBase.java
@@ -393,6 +393,8 @@
             switch (name) {
                 case BLUETOOTH_SERVICE:
                     return CarServiceTestApp.getAppContext().getSystemService(name);
+                case AUDIO_SERVICE:
+                    return CarServiceTestApp.getAppContext().getSystemService(name);
                 default:
                     return super.getSystemService(name);
             }