Explore ways to consolidate Checkstyle and Codenarc errors into single file for GitHub workflow

[jamesfredley]

Issue description

https://github.com/apache/grails-core/actions/runs/17872742072

Currently on the GitHub workflow you can download a zip with a file per subproject for Checkstyle and Codenarc with success and failure, which makes it difficult to quickly find the failure.

Locally the task output links you to the failure report(s)

[jdaugherty]

We parse out the rat errors and put them in the summary; something similar should be done for these. We may be able to change the codestyle plugin so that a single output directory can be found to make this easier.

[mika-collins]

I have raised PR #15486 to address the issue.