## 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



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ee/clickhouse/process_event.py
import datetime
import json
from typing import Dict, Optional
from uuid import UUID
import statsd
from celery import shared_task
from dateutil import parser
from dateutil.relativedelta import relativedelta
from django.conf import settings
from django.db.utils import IntegrityError
from ee.clickhouse.models.event import create_event
from ee.clickhouse.models.session_recording_event import create_session_recording_event
from ee.kafka_client.client import KafkaProducer
from ee.kafka_client.topics import KAFKA_EVENTS_WAL
from posthog.ee import is_ee_enabled
from posthog.models.element import Element
from posthog.models.person import Person
from posthog.models.team import Team
from posthog.models.utils import UUIDT
from posthog.tasks.process_event import handle_identify_or_alias, store_names_and_properties
if settings.STATSD_HOST is not None:
    statsd.Connection.set_defaults(host=settings.STATSD_HOST, port=settings.STATSD_PORT)
def _capture_ee(