## 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
github: bool = bool(settings.SOCIAL_AUTH_GITHUB_KEY and settings.SOCIAL_AUTH_GITHUB_SECRET)
    gitlab: bool = bool(settings.SOCIAL_AUTH_GITLAB_KEY and settings.SOCIAL_AUTH_GITLAB_SECRET)
    google: bool = False
    if getattr(settings, "SOCIAL_AUTH_GOOGLE_OAUTH2_KEY", None) and getattr(
        settings, "SOCIAL_AUTH_GOOGLE_OAUTH2_SECRET", None,
    ):
        if settings.MULTI_TENANCY:
            google = True
        else:
            try:
                from ee.models.license import License
            except ImportError:
                pass
            else:
                license = License.objects.first_valid()
                if license is not None and "google_login" in license.available_features:
                    google = True
                else:
                    print_warning(["You have Google login set up, but not the required premium PostHog plan!"])
    return {"google-oauth2": google, "github": github, "gitlab": gitlab}
def flatten(l: Union[List, Tuple]) -> Generator:
    for el in l:
        if isinstance(el, list):
            yield from flatten(el)
        else:
            yield el
def get_daterange(