## 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/views/actions.py
from posthog.models.cohort import Cohort
from posthog.models.entity import Entity
from posthog.models.filters import Filter
from posthog.models.property import Property
from posthog.models.team import Team
class ClickhouseActionSerializer(ActionSerializer):
    is_calculating = serializers.SerializerMethodField()
    def get_count(self, action: Action) -> Optional[int]:
        if self.context.get("view") and self.context["view"].action != "list":
            query, params = format_action_filter(action)
            if query == "":
                return None
            return sync_execute(
                "SELECT count(1) FROM events WHERE team_id = %(team_id)s AND {}".format(query),
                {"team_id": action.team_id, **params},
            )[0][0]
        return None
    def get_is_calculating(self, action: Action) -> bool:
        return False
    def _calculate_action(self, action: Action) -> None:
        
        pass
class ClickhouseActionsViewSet(ActionViewSet):
    serializer_class = ClickhouseActionSerializer
    def list(self, request: Request, *args: Any, **kwargs: Any) -> Response:
        actions = self.get_queryset()
        actions_list: List[Dict[Any, Any]] = self.serializer_class(actions, many=True, context={"request": request}).data  
        return Response({"results": actions_list})
    @action(methods=["GET"], detail=False)
    def people(self, request: Request, *args: Any, **kwargs: Any) -> Response: