Minor fixes for Python 3.12 compatibility
    
    - Fix Python unit tests to use the right assert methods
    - Explicitly BR python3-setuptools
    
    `distutils` is dropped in Python 3.12, but is provided in `setuptools`;
    even if we port `libkdumpfile` to use `setuptools` natively (not
    possible until `Extension` is ported) we'd need to depend on
    `setuptools` anyway.
    
    Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>