Suggestion: check minimum required Polylith version

[svdo]

The recent fix (💯) for #12 makes me suggest the following:

Since polylith-kaocha depends on a minimum version of clj-poly, it might be a good idea to check that and hard-fail (non-zero exit code). Because otherwise what happens is that no tests are run and exit code is zero, so for example in CI you might never notice that tests are not being run anymore.

Thanks again for all your good work! :)