Fix conftest.py compatibility with pytest 4.3
Fix conftest.py compatibility with pytest 4.3

While pytest in tox.ini is explicitly set to be 3.3.2, in Fedora 31
we are about to update to a newer version of pytest.
In order to be able to test babel, we need pytest 4.3 support.

This adds support for pytest 4.3 without breaking support for 3.3.2.

mitsuhiko/babel,mitsuhiko/babel,mitsuhiko/babel,python-babel/babel,python-babel/babel