Update comment in contravariant test

The current comment actually describes *co*-variance.
Fixing this to describe contravariance while keeping 'static in the definition was tricky so just changed to use 'short and 'long.

I found the typo in my attempt to understand the concept of variance itself and the comment confused me. I mention this to point out that I'm new to the concept so may have still got the definition wrong, so please review with care :)