function foundCircularReference (keyPath, $refs, options) {
$refs.circular = true;
if (!options.dereference.circular) {
  throw ono.reference('Circular $ref pointer found at %s', keyPath);
}
return true;
}
Called when a circular reference is found.
It sets the {@link $Refs#circular} flag, and throws an error if options.dereference.circular is false.

@param {string} keyPath - The JSON Reference path of the circular reference
@param {$Refs} $refs
@param {$RefParserOptions} options
@returns {boolean} - always returns true, to indicate that a circular reference was found