## 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
attr_id=el.get("attr__id"),
                nth_child=el.get("nth_child"),
                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", "ingested_event",
    ).get(pk=team_id)
    if not team.anonymize_ips and "$ip" not in properties:
        properties["$ip"] = ip
    Event.objects.create(
        event=event,
        distinct_id=distinct_id,
        properties=properties,
        team=team,
        site_url=site_url,
        **({"timestamp": timestamp} if timestamp else {}),
        **({"elements": elements_list} if elements_list else {})
    )
    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
def get_or_create_person(team_id: int, distinct_id: str) -> Tuple[Person, bool]: