Fix invocation with Python 3.9 (#1798929)
    
    Backported from Fedora 31:
    https://src.fedoraproject.org/rpms/python-tox/c/aa466cd2d67b5ca7e5f4f58d0fbc704b38c97d94?branch=f31
    
    Added 3.10 and 3.11 as well.
    
    With this tox.ini:
    
        [tox]
        skipsdist = True
        [testenv]
        commands = python -c 'import sys; print(sys.version)'
    
    Before:
    
        $ tox -e py39
        ...
        3.6.8 (default, Aug 24 2020, 17:57:11)
        ...
          py39: commands succeeded
          congratulations :)
    
    After:
    
        $ tox -e py39
        ...
        3.9.1 (default, Jan 18 2021, 16:14:01)
        ...
          py39: commands succeeded
          congratulations :)
    
    The Python 3.10+ addition remains untested, as I have no Python 3.10+ build for EL 8 available.