Bug#913524: python-xarray: failing autopkgtest with cftime 1.0.2

[Jeremy Bicha]

References
---------------
https://ci.debian.net/packages/p/python-xarray/unstable/amd64/
(In particular not the debci log for the first failure in October)
https://sources.debian.org/src/cftime/1.0.2.1-1/debian/changelog/

Thanks,
Jeremy Bicha