Delete .github/workflows/coana-guardrail.yml (#1237)

## Description

There is a serious [security
issue](https://www.stepsecurity.io/blog/harden-runner-detection-tj-actions-changed-files-action-is-compromised)
affecting the GitHub action tj-actions/changed-files, which
unfortunately is used by the coana-guardrail scanner. A malicious update
has changed the action to write secrets to the action log file, which
makes it particularly problematic for public repositories.

## Documentation

Does this require changes to the WorkOS Docs? E.g. the [API
Reference](https://workos.com/docs/reference) or code snippets need
updates.

```
[ ] Yes
```

If yes, link a related docs PR and add a docs maintainer as a reviewer.
Their approval is required.