[Iterable] customEvent 'data' field, which should hold json blobs, is all Null

### Connector Name

source-iterable

### Connector Version

0.6.53

### What step the error happened?

During the sync

### Relevant information

I have initialized a sync (both via PyAirbyte and the WebUI) to sync the custom_event data from Iterable to Snowflake. Unfortunately, every single row in the `data` column is `null` upon the completion of the sync.

I can make an API call to the iterable `/api/export/data.json` endpoint and get all of the custom event data I expect to, so I know the permissions of the API key are not the problem.

I also tried to pull the iterable.custom_event source data into a local `destination-csv` for testing purposes and found the same problem - every `_type` and `data` column value were null, leading me to believe that the issue is with the json parser which reads from the custom event API

### Relevant log output

```shell

```

### Contribute

- [ ] Yes, I want to contribute

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**Internal Tracking:** https://github.com/airbytehq/oncall/issues/11083