Sentry Issue: [POSTHOG-EU-3K](https://sentry.io/organizations/posthog/issues/3662211615/?referrer=github_integration)

```
ValidationError: {'events': [{'math': [ErrorDetail(string='"avg" is not a valid choice.', code='invalid_choice')]}]}
  File "posthog/api/insight.py", line 604, in trend
    serializer.is_valid(raise_exception=True)
  File "rest_framework/serializers.py", line 228, in is_valid
    raise ValidationError(self.errors)
```
posthog/models/entity/entity.py
"""
    Exclusion Entities represent Entities in Filter objects
    with extra parameters for exclusion semantics.
    """
    def __init__(self, data: Dict[str, Any]) -> None:
        super().__init__(data)
    def to_dict(self) -> Dict[str, Any]:
        ret = super().to_dict()
        for _, func in inspect.getmembers(self, inspect.ismethod):
            if hasattr(func, "include_dict"):  
                ret.update(func())
        return ret