When the Topic is set to "Enrollment created" in WordPress Dashboard > LifterLMS > Settings > REST API > Webhooks, the payload only contains information on 1 course (even though there are more than one enrollments that occurred).

### Reproduction Steps
1. Make at LifterLMS is the only plugin installed.
2. Login to the WordPress site as an administrator.
3. Create a membership called `Membership 1`.
4. Create three courses called `Course 1`, `Course 2`, and `Course 3`.
5. Open `Membership 1` in the backend and add `Course 1`, `Course 2`, and `Course 3` to `Membership Settings > Auto Enrollment`.
6. Add a free access plan to `Membership 1`.
7. Create a webhook in `WordPress Dashboard > LifterLMS > Settings > REST API > Webhooks` and set `Topic` to `Enrollment created`.
8. Use a free service like [webhook.site](https://webhook.site/) to generate the `Delivery URL` and to view the payload.
9. Create a student account in `WordPress Dashboard > Users > Add New`.
10. Log in as that student you created, and enroll on `Membership 1` while logged in as that student.
11. Got to [webhook.site](https://webhook.site/) to look at the payload.

### Expected Behavior
The payload should contain information about `Course 1`, `Course 2`, and `Course 3`.

### Actual Behavior
The payload contains information about `Course 1`.

This issue has be recreated:
+ [X] Locally
+ [] On a staging site
+ [X] On a production website
+ [X] With only LifterLMS and a default theme