Shell lint warnings cause workflow to fail

### TL;DR

The default abcxyz shell linter [ran against my PR](https://github.com/abcxyz/spanner-migrations/actions/runs/15430247702/job/43426510118?pr=3) and emitted only warnings as far as I can tell, but the workflow then failed with "Error: Process completed with exit code 123." [Raw logs here](https://gist.github.com/pjh/23fe9a39c59be4ae5327ef9c98576ae4).

My expectation is that warnings should not block PR submission, or there should at least be an easy way to bypass the warnings. If the messages should be blocking then they should be errors. Is there a way to adjust this?

### Expected behavior

_No response_

### Observed behavior

_No response_

### Environment Details

```markdown
GitHub
```

### Additional information

_No response_