added some failing tests for the Yoda fixer

You say it's just a matter of taste, but I disagree.
The idea is to prevent typos, which can occur in every `$var = non-var`, not only in `$var = constant`.

If it were merely a matter of taste, I wouldn't use Yoda conditions at all as I find they reduce readability. (`if 2 is my variable` vs. `if my variable is 2`)