## Bug description
I added an event (that exists) to an action, and now my action hangs forever.

I added an insight viewed event

w/ filters `insight == RETENTION` and `same_retention_and_cohortizing_event = false` – this appears to have broken my action where it does not load and I cannot edit it.

Cannot reproduce this same behavior locally.


## Expected behavior
- The action loads if the schema is correct.
-  If there's erroneous data it should load and let me edit it.

## How to reproduce

1. Create an action on Posthog cloud, in our main app
2. Add 'insight viewed' with filters `insight == RETENTION` and `same_retention_and_cohortizing_event = false`
3. The action will spin forever

## Environment

- [x] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: _please provide_

## Additional context

[Sentry error](https://sentry.io/organizations/posthog/issues/2378948964/?project=1899813&referrer=slack)

Console errors 
<img width="1607" alt="Screen Shot 2021-05-03 at 5 45 39 PM" src="https://user-images.githubusercontent.com/5965891/116950024-b0d7a280-ac38-11eb-93c8-245390240532.png">
<img width="1167" alt="Screen Shot 2021-05-03 at 5 51 34 PM" src="https://user-images.githubusercontent.com/5965891/116950026-b208cf80-ac38-11eb-96e1-6a8f018f650a.png">



#### *Thank you* for your bug report – we love squashing them!

ee/clickhouse/models/action.py
if entity.type == TREND_FILTER_TYPE_ACTIONS:
        try:
            action = Action.objects.get(pk=entity.id)
            entity_filter, params = format_action_filter(action, prepend=prepend, filter_by_team=filter_by_team)
        except Action.DoesNotExist:
            raise ValueError("This action does not exist")
    else:
        key = f"{prepend}_event"
        entity_filter = f"event = %({key})s"
        params = {key: entity.id}
    return entity_filter, params