Two write tests fail after an update of *python-eccodes*

[alexamici]

The tests test_50_sample_data.py::test_canonical_dataset_to_grib[era5-levels-members] and test_50_sample_data.py::test_canonical_dataset_to_grib[regular_ll_msl] fail the round trip test.

We observe waring like:

WARNING  cfgrib.messages:messages.py:171 failed to set key 'number' to 0
WARNING  cfgrib.messages:messages.py:171 failed to set key 'endStep' to numpy.timedelta64(0,'ns')

This points to the wrong GRIB message to be use as template, that probably happen after an update to python-eccodes but it is not possible to test the old version because it has been removed by conda forge.

I'll add xfail makers for now.

[iainrussell]

This will be partly fixed with python-eccodes 1.4.1 - the problem with encoding the 'number' was that it is a numpy.int64 (a side-effect of #272), which python-eccodes did not accept. The next python-eccodes will accept it. I have a separate fix in cfgrib for the 'endStep' issue, and with that, these tests should work again.

[iainrussell]

With the latest commit and python-eccodes 1.4.1, these two tests will work again. I will not re-activate them and close this issue until python-eccodes has been released.