## 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!

posthog/models/filters/test/test_filter.py
event_factory(team=self.team, distinct_id="test", event="$pageview")
            event2 = event_factory(
                team=self.team, event="$pageview", distinct_id="test", properties={"is_first": True},
            )
            filter = Filter(data={"properties": {"is_first": "true"}})
            events = filter_events(filter, self.team)
            self.assertEqual(events[0]["id"], event2.pk)
            filter = Filter(data={"properties": {"is_first": ["true"]}})
            events = filter_events(filter, self.team)
            self.assertEqual(events[0]["id"], event2.pk)
        def test_is_not_true_false(self):
            event = event_factory(team=self.team, distinct_id="test", event="$pageview")
            event2 = event_factory(
                team=self.team, event="$pageview", distinct_id="test", properties={"is_first": True},
            )
            filter = Filter(data={"properties": [{"key": "is_first", "value": "true", "operator": "is_not"}]})
            events = filter_events(filter, self.team)
            self.assertEqual(events[0]["id"], event.pk)
        def test_json_object(self):