Temporarily mark pseudonetcdf-3.1 as incompatible (#3420)

Author: crusaderky

ci/requirements/py36.yml

@@ -29,7 +29,7 @@ dependencies:
   - pandas
   - pint
   - pip
-  - pseudonetcdf
+  - pseudonetcdf<3.1  # FIXME https://github.com/pydata/xarray/issues/3409
   - pydap
   - pynio
   - pytest

ci/requirements/py37-windows.yml

@@ -29,7 +29,7 @@ dependencies:
   - pandas
   - pint
   - pip
-  - pseudonetcdf
+  - pseudonetcdf<3.1  # FIXME https://github.com/pydata/xarray/issues/3409
   - pydap
   # - pynio  # Not available on Windows
   - pytest

ci/requirements/py37.yml

@@ -29,7 +29,7 @@ dependencies:
   - pandas
   - pint
   - pip
-  - pseudonetcdf
+  - pseudonetcdf<3.1  # FIXME https://github.com/pydata/xarray/issues/3409
   - pydap
   - pynio
   - pytest