## Bug description

There seems to be an issue with `get_available_timezones_with_offsets`, not sure at what point it broke.

```
Traceback (most recent call last):
    response = view_func(request, *args, **kwargs)
  File "/posthog/posthog/views.py", line 184, in preflight_check
    "available_timezones": get_available_timezones_with_offsets(),
    raise NonExistentTimeError(dt)
```

## Expected behavior
Preflight should work and the timezone list be returned correctly.


## How to reproduce

1. Just check `/_preflight` request

## Environment

- [X] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: _please provide_

## Additional context

Tagging @Twixes as you have more context on this.

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

posthog/utils.py
start_date: Optional[datetime.datetime], end_date: Optional[datetime.datetime], frequency: str
) -> List[Any]:
    """
    Returns list of a fixed frequency Datetime objects between given bounds.
    Parameters:
        start_date: Left bound for generating dates.
        end_date: Right bound for generating dates.
        frequency: Possible options => minute, hour, day, week, month
    """
    delta = DATERANGE_MAP[frequency]
    if not start_date or not end_date:
        return []
    time_range = []
    if frequency != "minute" and frequency != "hour":
        start_date = start_date.replace(hour=0, minute=0, second=0, microsecond=0)
        end_date = end_date.replace(hour=0, minute=0, second=0, microsecond=0)
    if frequency == "week":
        start_date += datetime.timedelta(days=6 - start_date.weekday())
    if frequency != "month":
        while start_date <= end_date:
            time_range.append(start_date)
            start_date += delta
    else:
        if start_date.day != 1:
            start_date = (start_date.replace(day=1) + delta).replace(day=1)
        while start_date <= end_date:
            time_range.append(start_date)
            start_date = (start_date.replace(day=1) + delta).replace(day=1)
    return time_range
def get_safe_cache(cache_key: str):