SFML convention is to only use "" includes when the header is in
the same directory as the file including it. Because these test
util headers are in a separate directory, it makes more sense to
include them via <>.
This ensures that if a printing function is not provided, compilation
fails. This prevents problems where a header is accidentally removed
that was previously providing an operator<< overload or prevents
new tests from being added without print support for all directly
tested types.
