## Bug description

If I mark an insight as a favorite (⭐) and then refresh, the insight is no longer marked as a favorite although it is (can see it in Favorites).

<img width="390" alt="image" src="https://user-images.githubusercontent.com/30181361/182802236-9ecf0531-899c-4f25-ae86-bc233cefdc2f.png">

Note that I'm in the _Favorites_ tab and that _Bug example_ is not starred.
## Environment

- [x] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: please provide

posthog/api/insight.py
try:
            before_update = Insight.objects.prefetch_related("tagged_items__tag", "dashboards").get(pk=instance.id)
        except Insight.DoesNotExist:
            before_update = None
        
        validated_data["is_sample"] = False
        if validated_data.keys() & Insight.MATERIAL_INSIGHT_FIELDS:
            instance.last_modified_at = now()
            instance.last_modified_by = self.context["request"].user
        if validated_data.get("deleted", False):
            DashboardTile.objects.filter(insight__id=instance.id).delete()
        else:
            dashboards = validated_data.pop("dashboards", None)
            if dashboards is not None:
                old_dashboard_ids = [tile.dashboard_id for tile in instance.dashboardtile_set.all()]
                new_dashboard_ids = [d.id for d in dashboards]
                ids_to_add = [id for id in new_dashboard_ids if id not in old_dashboard_ids]
                ids_to_remove = [id for id in old_dashboard_ids if id not in new_dashboard_ids]
                
                
                dashboard: Dashboard