Enable warnings-as-errors for cuproj tests

[mroeschke]

Description

Following https://github.com/rapidsai/build-planning/issues/26, enabled warnings-as-errors for cuproj test

Checklist

• [ ] I am familiar with the Contributing Guidelines.
• [ ] New or existing tests cover these changes.
• [ ] The documentation is up to date with these changes.

[bdice]

/merge