`up --frozen-lockfile` doesn't fail when lockfile is outdated

`npx @devcontainers/cli up --help` says:
```
--frozen-lockfile Ensure lockfile exists and remains unchanged;
fail otherwise. [boolean] [default: false]
```

I just ran `up --frozen-lockfile` twice, changing `devcontainer.json` (Really simple - image and feature. Changed feature from one to another.) in between without updating the lockfile. Got success and the same container id both times.