## 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
from django.db import connection
    query = f"SELECT reltuples::BIGINT as \"approx_count\" FROM pg_class WHERE relname = '{table_name}'"
    cursor = connection.cursor()
    cursor.execute(query)
    return dict_from_cursor_fetchall(cursor)
def is_postgres_alive() -> bool:
    from posthog.models import User
    try:
        User.objects.count()
        return True
    except DatabaseError:
        return False
def is_redis_alive() -> bool:
    try:
        get_redis_info()
        return True
    except BaseException:
        return False
def is_celery_alive() -> bool:
    try:
        return get_celery_heartbeat() != "offline"
    except BaseException:
        return False
def is_plugin_server_alive() -> bool: