Set Android T as default target for APK signing key rotation am: 6ad4c757ab am: 107fff999e am: e370b67c74

Original change: https://googleplex-android-review.googlesource.com/c/platform/tools/apksig/+/18084651

Change-Id: Id1423a993bc8d2a7b51a10982005212b25b9abee
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>