## Bug description
 
It looks like either timestamp or sent_at is being sent without timezone, causing [this issue](https://sentry.io/organizations/posthog/issues/1972106098/?project=1899813&query=is%3Aunresolved&statsPeriod=14d)

## Expected behavior

It should send both timestamps with timezone

## How to reproduce

1. 
2. 
3. 

## Environment

- PostHog cloud or self-managed?
- PostHog version/commit

## Additional context



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

posthog/tasks/process_event.py
save = False
    if not team.ingested_event:
        
        for user in Team.objects.get(pk=team.pk).users.all():
            posthoganalytics.capture(user.distinct_id, "first team event ingested", {"team": str(team.uuid)})
        team.ingested_event = True
        save = True
    if event not in team.event_names:
        save = True
        team.event_names.append(event)
    for key, value in properties.items():
        if key not in team.event_properties:
            team.event_properties.append(key)
            save = True
        if isinstance(value, Number) and key not in team.event_properties_numerical:
            team.event_properties_numerical.append(key)
            save = True
    if save:
        team.save()
def _capture(