Fix deprecated use of dispatch event

The arguments are called the wrong way around. This still works but is deprecated in Drupal 9.1.

In HostedFields::createPayment():

// Add metadata and extra transaction data where required.
$event = new TransactionDataEvent($transaction_data, $payment);
$this->eventDispatcher->dispatch(BraintreeEvents::TRANSACTION_DATA, $event);

Results in:
@trigger_error('Calling the Symfony\Component\EventDispatcher\EventDispatcherInterface::dispatch() method with a string event name as the first argument is deprecated in drupal:9.1.0, an Event object will be required instead in drupal:10.0.0. See https://www.drupal.org/node/3154407', E_USER_DEPRECATED);