## 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
if data.get("timestamp"):
        if sent_at:
            
            
            try:
                
                
                return now + (parser.isoparse(data["timestamp"]) - sent_at)
            except TypeError as e:
                pass
        return parser.isoparse(data["timestamp"])
    now_datetime = now
    if data.get("offset"):
        return now_datetime - relativedelta(microseconds=data["offset"] * 1000)
    return now_datetime
if is_ee_enabled():
    def process_event_ee(