Select only one version of each dataset

[bouweandela]

The problem

There appear to be two versions of the same dataset selected for the climate drivers for fire diagnostic:

climate-ref/packages/climate-ref-esmvaltool/tests/unit/test_solve_regression/test_solve_regression_climate_drivers_for_fire_.yml

Lines 96 to 97 in 5c0817f

	- CMIP6.CMIP.EC-Earth-Consortium.EC-Earth3-Veg.historical.r1i1p1f1.Amon.tas.gr.v20200225
	- CMIP6.CMIP.EC-Earth-Consortium.EC-Earth3-Veg.historical.r1i1p1f1.Amon.tas.gr.v20211207

Definition of "done"

Only one version of each dataset should be included in the result of a solve. Maybe only the latest version, so CMIP6.CMIP.EC-Earth-Consortium.EC-Earth3-Veg.historical.r1i1p1f1.Amon.tas.gr.v20211207 and not CMIP6.CMIP.EC-Earth-Consortium.EC-Earth3-Veg.historical.r1i1p1f1.Amon.tas.gr.v20200225

Additional context

[lewisjared]

I'll have to check if this is an issue with how the data catalog is produced/used. When solving we remove the duplicate versions, but that code path might not be followed for the test case.