ci: use python2 version of pytest
    
    Fedora 31 changed symlink of /usr/bin/py.test from pytest2 to pytest3.
    We need to run the python2 version in order to run our tests with python2.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    
    Reviewed-by: Tomáš Halman <thalman@redhat.com>