## 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
key = request.GET.get("key")
        value = request.GET.get("value")
        select_regex = '[:|"]{}="(.*?)"'.format(key)
        
        if key not in self.serializer_class.Meta.fields:
            return response.Response([])
        if key == "tag_name":
            select_regex = "^([-_a-zA-Z0-9]*?)[\.|:]"
            filter_regex = select_regex
            if value:
                filter_regex = "^([-_a-zA-Z0-9]*?{}[-_a-zA-Z0-9]*?)[\.|:]".format(value)
        else:
            if value:
                filter_regex = '[:|"]{}=".*?{}.*?"'.format(key, value)
            else:
                filter_regex = select_regex
        result = sync_execute(
            GET_VALUES.format(), {"team_id": self.team.id, "regex": select_regex, "filter_regex": filter_regex}
        )
        return response.Response([{"name": value[0]} for value in result])