Fixes flaky test found in nightly run: https://github.com/fleetdm/fleet/actions/runs/30330273165. <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **Tests** * Improved execution checks to tolerate transient busy-file errors during retries. * Strengthened validation for both healthy and corrupted binaries, ensuring tests report the intended result. <!-- end of auto-generated comment: release notes by coderabbit.ai -->