Emit a warning instead of aborting am: 1c21eb8364 am: 1ccbd1d5a8

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1626659

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I922edb1b4be669bdf06c7fb6eb8a15bcab900dc4