Add support for post-submit-only ART gtests to `regen-test-files`. am: cda59b5354

Original change: https://android-review.googlesource.com/c/platform/art/+/2962582

Change-Id: I959c14875cd5ae0a29fee10b43bafcef9236aa0c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>