## Bug description

Deprecation warning due to invalid escape sequences in Python 3.8 . 

```
posthog/models/team.py:47:46: W605 invalid escape sequence '\w'
posthog/models/filters/test/test_filter.py:131:74: W605 invalid escape sequence '\.'
posthog/models/filters/test/test_filter.py:135:78: W605 invalid escape sequence '\.'
posthog/migrations/0132_team_test_account_filters.py:51:46: W605 invalid escape sequence '\w'
ee/clickhouse/views/element.py:47:48: W605 invalid escape sequence '\.'
ee/clickhouse/views/element.py:50:69: W605 invalid escape sequence '\.'
```

This is little more important since Python emits deprecation warning during compile time for these

## Expected behavior

This can be fixed with pyupgrade : https://github.com/asottile/pyupgrade#invalid-escape-sequences . Appropriate rule can be added to flake8 so that this caught.

## How to reproduce


```
find posthog -iname '*py' | xargs -P4 -I{} python3.8 -Wall -m py_compile {}     
posthog/models/team.py:47: DeprecationWarning: invalid escape sequence \w
  example_email = re.search("@[\w.]+", example_emails[0])
posthog/models/filters/test/test_filter.py:131: DeprecationWarning: invalid escape sequence \.
  filter = Filter(data={"properties": {"$current_url__regex": "\.com$"}})
posthog/models/filters/test/test_filter.py:135: DeprecationWarning: invalid escape sequence \.
  filter = Filter(data={"properties": {"$current_url__not_regex": "\.eee$"}})
posthog/migrations/0132_team_test_account_filters.py:51: DeprecationWarning: invalid escape sequence \w
  example_email = re.search("@[\w.]+", example_emails[0])
```

## Environment

- [ ] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: _please provide_

## Additional context



#### *Thank you* for your bug report – we love squashing them!

ee/clickhouse/views/element.py
@action(methods=["GET"], detail=False)
    def stats(self, request: request.Request, **kwargs) -> response.Response:
        filter = Filter(request=request)
        date_from, date_to, _ = parse_timestamps(filter, team_id=self.team.pk)
        prop_filters, prop_filter_params = parse_prop_clauses(filter.properties, self.team.pk)
        result = sync_execute(
            GET_ELEMENTS.format(date_from=date_from, date_to=date_to, query=prop_filters),
            {"team_id": self.team.pk, **prop_filter_params},
        )
        return response.Response(
            [
                {
                    "count": elements[1],
                    "hash": None,
                    "elements": [ElementSerializer(element).data for element in chain_to_elements(elements[0])],
                }
                for elements in result
            ]
        )
    @action(methods=["GET"], detail=False)
    def values(self, request: request.Request, **kwargs) -> response.Response: