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

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



Change-Id: I08029f10a512705bbed29653c7dbfdb503b10f52
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>