Bug#1022571: transition: pandas 1.3 -> 1.5

[Rebecca N. Palmer]

The remaining autopkgtest failures blocking pandas are:
- dipy/amd64 and snakemake/i386 look like random flakiness: please retry 
them.  (I think DMs can't use the self-service interface.)  Or for dipy, 
see #1029533 for a possible fix.
- python-xarray/i386 looks like xarray not pandas: see #1004869.
- dask and dask.distributed have to go together, with or before pandas.