Tmux 3 raises "invalid option" on an invalid option

Hi,

The following test:

def test_show_option_unknown(session):
    """Session.show_option raises UnknownOption for invalid option."""
    with pytest.raises(exc.UnknownOption):
        session.show_option('moooz')

in tests/test_session.py

fails because my version of tmux (3.1b) prints "invalid option: moooz" when given an invalid option.

I have no easy way to test whether tmux 2's behaviour was to throw an "unknown option" instead.

I don't know how you want to fix this. Shall we throw a UnknownOption to maintain backwards compatibility (is any one try...excepting for this specifically anyway ?) Shall we remove this test now that tmux has changed its ways ?

Start with tests/test_session.py and reproduce test_show_option_unknown using tmux 3.1b. Trace session.show_option and compare the exception produced for the invalid option, then determine the compatible behavior for supported tmux versions. Done means the test and exception behavior are consistent with the chosen compatibility decision.