Bug#1088988: pandas: FTBFS with xarray 2024.11.0 (test failures)

[Rebecca N. Palmer]

Control: retitle -1 pandas<->xarray data conversion issues
Control: affects -1 python3-xarray

After fixing the easy parts (see Salsa), there are 3 remaining issues:

- Datetime-with-timezone, categorical, python-string, and nullable 
indices lose this dtype (becoming object dtype, keeping their values; 
note that none of the nullable indices tested actually contain nulls) 
when going from pandas to xarray.
- For datetime-with-timezone indices (but not the other cases with the 
above issue), the values of the categorical column (but not all the 
columns) are lost, replaced by NaNs.  As the xarray object does not 
display this column's values, I do not know which step this happens at. 
*Possibly* related to the exception when *all* columns are nullable 
reported in upstream https://github.com/pydata/xarray/issues/9661 .
- If the index contains duplicate values, each row gets repeated as many 
times as there are rows with that index value, when going from xarray to 
pandas.  Not obviously known upstream.