Specify FLAG_IMMUTABLE when creating PendingIntent am: 6f7d23a503 am: 4aa8e9a668 am: 0800a8ab8e

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Car/SystemUpdater/+/15113943

Change-Id: I32fce92d1d850ef3057dca622c533c4c732d5808