[automerge] [RESTRICT AUTOMERGE][pm] still allow debuggable for system app downgrades 2p: 636cdf22b9

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/21266989

Bug: 267232653
Bug: 256202273
Change-Id: Iba1c01bf07da821a05d3439df54e811ccfdf4505