## Bug description

I have lost edit permissions to a [dashboard I created](https://app.posthog.com/dashboard/28987), despite still being listed as the owner of the dashboard

## Expected behavior

I should still be able to edit the dashboard

## How to reproduce

I noticed this problem after adding a new insight, but this doesn't appear to be the cause of the issue. I've duplicated the dashboard to restore access and adding a new insight didn't appear to cause the issue 

## Environment

- [x] PostHog Cloud
- [ ] self-hosted PostHog (ClickHouse-based), version/commit: _please provide_
- [ ] self-hosted PostHog (Postgres-based, legacy), version/commit: _please provide_

## Additional context

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

posthog/api/insight.py
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
        return super().update(instance, validated_data)
    def get_result(self, insight: Insight):
        if not insight.filters:
            return None
        if self.context["request"].GET.get("refresh"):
            return update_dashboard_item_cache(insight, None)
        result = get_safe_cache(insight.filters_hash)
        if not result or result.get("task_id", None):
            return None
        
        return result.get("result")
    def get_last_refresh(self, insight: Insight):
        if self.context["request"].GET.get("refresh"):
            return now()
        result = self.get_result(insight)
        if result is not None:
            return insight.last_refresh
        if insight.last_refresh is not None:
            
            insight.last_refresh = None
            insight.save()
        return None
    def get_effective_privilege_level(self, insight: Insight) -> Dashboard.PrivilegeLevel:
        return insight.get_effective_privilege_level(self.context["request"].user)
    def to_representation(self, instance: Insight):