[RESTRICT AUTOMERGE][pm] still allow debuggable for system app downgrades am: 14a91d2bc8

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

Change-Id: Iab1bdd92f923fef44dca6b3e259e4867ee7f8d8c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>