trusty:cast-test: only run keybox test when using matching fake keybox am: 7109dd4b61

Original change: https://android-review.googlesource.com/c/trusty/app/cast-auth/+/2950545

Change-Id: Id36d5bea15f5553f45eb8945fdd8f99c8234be48
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>