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

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

Change-Id: Ibefbe2af1275543af6de008d4cd25646d5fb1c57