List membership enrollments always returns 404

### Reproduction Steps

Perform a GET request to the /`memberships/{id}/enrollments` endpoint using any valid membership post id

### Expected Behavior

A collection of enrollments for the given membership is returned

### Actual Behavior

The API returns 404 `llms_rest_not_found`

### Error Messages / Logs

```
{
"code": "llms_rest_not_found",
"message": "The requested resource could not be found.",
"data": {
"status": 404
}
}

```

### System Information

System Report

```
LifterLMS Rest API 1.0.0-beta.12
```