Skip failing test on JRuby.
Skip failing test on JRuby.

On JRuby, FFI.find_type generates a new wrapper for enums every time it is
called. Therefore, this test will always fail there. Skip it instead.

jcupitt/gir_ffi,jcupitt/gir_ffi,mvz/gir_ffi,mvz/gir_ffi,mvz/gir_ffi