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
import inspect
from typing import Any, Counter, Dict, Literal, Optional, Union
from django.conf import settings
from rest_framework.exceptions import ValidationError
from posthog.constants import TREND_FILTER_TYPE_ACTIONS, TREND_FILTER_TYPE_EVENTS
from posthog.models.action import Action
from posthog.models.filters.mixins.funnel import FunnelFromToStepsMixin
from posthog.models.filters.mixins.property import PropertyMixin
from posthog.models.filters.utils import validate_group_type_index
from posthog.models.property import GroupTypeIndex
from posthog.models.utils import sane_repr
MathType = Literal[
    "total",
    "dau",
    "weekly_active",
    "monthly_active",
    "unique_group",
    "unique_session",
    "sum",
    "min",
    "max",
    "median",