update JUWELS req, xarray

HPC_setup/requirements_JUWELS_outcommented.txt

@@ -61,6 +61,6 @@ statsmodels==0.11.1              # (in Jupyter, but not found)
 # urllib3==1.25.8                # in Python
 # wcwidth==0.1.8                 # in Python 
 # Werkzeug==1.0.0                # in python
-# xarray==0.15.0                 # in SciPy-Stack
+xarray==0.15.0                 # in SciPy-Stack only 0.12.1 a
 # zipp==3.1.0                    # in Jupyter
 tabulate