[RESTRICT AUTOMERGE][pm] still allow debuggable for system app downgrades am:...

[RESTRICT AUTOMERGE][pm] still allow debuggable for system app downgrades am: 14a91d2b am: dbd81bcb am: 8ea97800

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21266935



Change-Id: Ibe3e160facc49fb7919ada0944f8561fabe32cdd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>