Update package pytest to 6.2

[taldcroft]

Update package pytest to 6.2

This release includes a very useful improvement to show the reason for a skip or xfail in verbose mode. This was a 4-year old issue that finally got fixed. In addition it has a new temp dir test fixture that it is a Path instead of a py.path.local thingy.

https://docs.pytest.org/en/stable/changelog.html#pytest-6-2-0-2020-12-12

On the flip side pytest makes so many breaking changes that we'll have to check that it doesn't break too many tests (though we don't really scratch the surface of pytest functionality).