[BUG] build_message outputs "All tests successful" if there is exactly one failure

[mikkokeskinen]

If there is exactly one failure, the build_message function outputs:

✅ All tests successful. No failed tests were found.

Because in the templates/test_results_message.md there is a wrong if clause:

{% if num_failed > 1 %}

It should obviously be

{% if num_failed > 0 %}