Tests: Cope with different invocation methods
    
    Depending on how the tests are run (`pytest`, `python -m pytest`, ...),
    the program name can be e.g. `pytest` or `pytest.py`. Relax the relevant
    tests a bit, this way we don't have to update them every time we change
    something related to CLI arguments either.
    
    Signed-off-by: Nils Philippsen <nils@redhat.com>