## 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!

ee/clickhouse/process_event.py
nth_of_type=el.get("nth_of_type"),
                attributes={key: value for key, value in el.items() if key.startswith("attr__")},
            )
            for index, el in enumerate(elements)
        ]
    team = Team.objects.only("slack_incoming_webhook", "event_names", "event_properties", "anonymize_ips").get(
        pk=team_id
    )
    if not team.anonymize_ips and "$ip" not in properties:
        properties["$ip"] = ip
    store_names_and_properties(team=team, event=event, properties=properties)
    if not Person.objects.distinct_ids_exist(team_id=team_id, distinct_ids=[str(distinct_id)]):
        
        
        try:
            Person.objects.create(team_id=team_id, distinct_ids=[str(distinct_id)])
        except IntegrityError:
            pass
    
    create_event(
        event_uuid=event_uuid,
        event=event,
        properties=properties,
        timestamp=timestamp,
        team=team,
        distinct_id=distinct_id,
        elements=elements_list,
        site_url=site_url,
    )
def handle_timestamp(data: dict, now: datetime.datetime, sent_at: Optional[datetime.datetime]) -> datetime.datetime: