[Components][Event Dispatcher] Fix "store.order" event name in code example

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | -

The name of the event in this example is ``store.event``; ``STORE_ORDER`` is used for the class constant in ``StoreEvents::STORE_ORDER``.