pylint: Replace deprecated extension-pkg-whitelist
    
    `extension-pkg-whitelist` is deprecated in favour of
    `extension-pkg-allow-list` since Pylint 2.7.3:
    https://pylint.pycqa.org/en/latest/whatsnew/2/2.7/full.html#what-s-new-in-pylint-2-7-3
    
    Fixes: https://pagure.io/freeipa/issue/9278
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Stanislav Levin <slev@altlinux.org>