Fix test_config_initialization to be correctly skipped on pytest<5,
by explicitly checking pytest version (idea copied from
test_looponfail_removed_test). The current conditions are insufficient
-- the outer check wrongly assumes pytest>=5 will always be used
on Python 3 (which is not true if you need the same version to support
both Python 2 and Python 3), and the inner condition apparently
wrongly assuming that invocation_params attribute is not present
in pytest-4.
94bdd18a03