test(cli): pin the os migrate family's unmet-confirmation exit code

Every migrate subcommand that writes behind a confirmation, discovered
from its flags, answers a non-interactive run without it with exit 1 in
both faces, names its confirmation flag, and reaches no write seam.

Claude-Session: https://claude.ai/code/session_01LmjU2x1faLZ39DVTFyVca6
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude