## 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
response = self.client.post(
            "/batch/",
            data={
                "api_key": "this-token-doesnt-exist",
                "batch": [{"type": "capture", "event": "user signed up", "distinct_id": "whatever",},],
            },
            content_type="application/json",
        )
        self.assertEqual(response.status_code, 400)
        self.assertEqual(
            response.json()["message"],
            "API key is incorrect. You can find your API key in the /setup page in PostHog.",
        )
    def test_batch_token_not_set(self):