## Bug description

While exploring the onboarding/setup funnel, I found what seems to be a bug capturing events (perhaps it's an API request issue). When I send this request, the events don't get saved (checked directly on the database).

```
POST <host>/capture
```

```json
{
    "api_key": "API_KEY_HERE",
    "event": "Purchase item",
    "properties": {
        "distinct_id": "845555992929291"
    }
}
```


## Expected behavior
- Events should be correctly saved to the database. If on the onboarding flow, continue the user and complete the onboarding.
- If the request is malformed or an invalid API key is sent, I should not receive a 200 status code. _There seems to be an issue with the request and therefore the event is not saved_, however **if I add a random non-existent key as the API key (e.g. `invalid`), I still get a 200 and a 1 in the response.**  


## Reproduction environment
- Tested using the one-line Docker deploy.
```bash
doker run -t -i --rm --publish 8000:8000 -v postgres:/var/lib/postgresql posthog/posthog:preview
```
- Tested on the cloud version with the same result (please reach out privately if you want to know the account's email address).

posthog/api/test/test_capture.py
data = {
            "api_key": self.team.api_token,
            "batch": [{"type": "capture", "event": "user signed up", "distinct_id": "2"}],
        }
        response = self.client.generic(
            "POST",
            "/batch/?compression=gzip",
            data=gzip.compress(json.dumps(data).encode()),
            content_type="application/json",
        )
        arguments = patch_process_event.call_args[1]
        arguments.pop("now")  # c
        arguments.pop("sent_at")  # c
        self.assertDictEqual(
            arguments,
            {
                "distinct_id": "2",
                "ip": "127.0.0.1",
                "site_url": "http://testserver",
                "data": data["batch"][0],
                "team_id": self.team.pk,
            },
        )
    @patch("posthog.models.team.TEAM_CACHE", {})
    @patch("posthog.tasks.process_event.process_event.delay")
    def test_batch_lzstring(self, patch_process_event):