Fix kotlin nullable errors in TrustTests

Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.

Bug: 294110802
Test: builds
Change-Id: I31c4f4d256ff8dd2b6ed1f6ed74844ccaf7a4814
Merged-In: I31c4f4d256ff8dd2b6ed1f6ed74844ccaf7a4814
(cherry picked from commit c5a0cfdd)