Run bmi-test on unix only
Run bmi-test on unix only

There may be a problem upstream with gridmet_bmi not closing a netCDF
data file. This is from the conda-forge Windows build:
```
E   PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'C:\\Users\\VssAdministrator\\.gridmet\\daily_maximum_temperature_2020-01-01_2020-01-07.nc'
```

jakirkham/staged-recipes,ReimarBauer/staged-recipes,goanpeca/staged-recipes,johanneskoester/staged-recipes,goanpeca/staged-recipes,ocefpaf/staged-recipes,patricksnape/staged-recipes,hadim/staged-recipes,stuertz/staged-recipes,patricksnape/staged-recipes,mariusvniekerk/staged-recipes,johanneskoester/staged-recipes,hadim/staged-recipes,scopatz/staged-recipes,kwilcox/staged-recipes,jochym/staged-recipes,stuertz/staged-recipes,igortg/staged-recipes,jochym/staged-recipes,kwilcox/staged-recipes,conda-forge/staged-recipes,mariusvniekerk/staged-recipes,scopatz/staged-recipes,conda-forge/staged-recipes,ocefpaf/staged-recipes,igortg/staged-recipes,jakirkham/staged-recipes,ReimarBauer/staged-recipes