Specify FLAG_IMMUTABLE when creating PendingIntent

Targeting S+ (version 31 and above) requires that one of
FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a
PendingIntent. So this CL uses FLAG_IMMUTABLE to create
the PendingIntent because the flag is recommended in most cases.

Bug: 192103710
Test: manual
Change-Id: Ic5396ca753bfdf3d1e616511cd64490b22f58e59
diff --git a/tests/usb/AoapPhoneCompanionApp/src/com/google/android/car/usb/aoap/companion/AoapPhoneCompanionActivity.java b/tests/usb/AoapPhoneCompanionApp/src/com/google/android/car/usb/aoap/companion/AoapPhoneCompanionActivity.java
index f71a575..408271e 100644
--- a/tests/usb/AoapPhoneCompanionApp/src/com/google/android/car/usb/aoap/companion/AoapPhoneCompanionActivity.java
+++ b/tests/usb/AoapPhoneCompanionApp/src/com/google/android/car/usb/aoap/companion/AoapPhoneCompanionActivity.java
@@ -124,7 +124,7 @@
             Intent intent = new Intent(ACTION_USB_ACCESSORY_PERMISSION);
             intent.setPackage(getPackageName());
             PendingIntent pendingIntent = PendingIntent.getBroadcast(
-                    this, 0, intent, PendingIntent.FLAG_ONE_SHOT);
+                    this, 0, intent, PendingIntent.FLAG_IMMUTABLE | PendingIntent.FLAG_ONE_SHOT);
             mUsbManager.requestPermission(accessory, pendingIntent);
             return;
         }