Refactor FRE make null tests configurations

[singhd789]

Is your feature request related to a problem? Please describe.
Recent FMS code changes have broken the fre-cli fre make pipeline, causing issues unrelated to the unit tests.

See pipeline failures here: https://github.com/NOAA-GFDL/fre-cli/actions/runs/20971755444/job/60276624265?pr=691

Describe the solution you'd like
FRE make tests should not include actual model code (Seth's suggestion). It should be a very simple test that can compile a model.