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'
```
@@ -30,7 +30,7 @@ test:
imports:
- pymt_gridmet
commands:
- - bmi-test pymt_gridmet.bmi:GridMet -vvv
+ - bmi-test pymt_gridmet.bmi:GridMet -vvv # [unix]
about:
home: https://github.com/pymt-lab/pymt_gridmet
