Test with negative and 0 lengths sides of invalid triangles

[szabgab]

I've encountered solution where the student only checked if the sides are 0 and not if they are negative. In other cases only one of the functions was checking if the triangle is even valid.

I submitted some additional tests for the Python track https://github.com/exercism/python/pull/2704 , but was pointed to this file: https://github.com/exercism/problem-specifications/blob/main/exercises/triangle/canonical-data.json Before adding those tests to the json file, I'd like to know if you think those should be added or it is ok if people only check for 0 length sides.