## 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
if old_person and not new_person:
        try:
            old_person.add_distinct_id(distinct_id)
        
        except IntegrityError:
            if retry_if_failed:  
                _alias(previous_distinct_id, distinct_id, team_id, False)
        return
    if not old_person and new_person:
        try:
            new_person.add_distinct_id(previous_distinct_id)
        
        except IntegrityError:
            if retry_if_failed:  
                _alias(previous_distinct_id, distinct_id, team_id, False)
        return
    if not old_person and not new_person:
        try:
            Person.objects.create(
                team_id=team_id, distinct_ids=[str(distinct_id), str(previous_distinct_id)],
            )
        
        except IntegrityError:
            if retry_if_failed:
                
                _alias(previous_distinct_id, distinct_id, team_id, False)
        return
    if old_person and new_person and old_person != new_person:
        new_person.merge_people([old_person])
def store_names_and_properties(team: Team, event: str, properties: Dict) -> None: