Modifying abl_sampling reg test to avoid NetCDF error

[mbkuhn]

Summary

Specifying velocity as a sampling field and velocity components as derived fields doesn't produce issues in the mechanics of AMR-Wind, but it creates redundant variable names that produce a conflict in NetCDF. "NetCDF: String match to name in use". This avoids that error

Pull request type

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe):

Checklist

The following is included:

• [ ] new unit-test(s)
• [ ] new regression test(s)
• [ ] documentation for new capability

This PR was tested by running:

• the unit tests
  • [ ] on GPU
  • [ ] on CPU
• the regression tests
  • [ ] on GPU
  • [x] on CPU

[mbkuhn]

@marchdf feel free to correct me if you can't reproduce this error, but this was popping up when running the reg tests locally

[marchdf]

I wasn't seeing this before... let me try locally.

[mbkuhn]

gonna put checks in the code instead