## 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
person1 = person_factory(team_id=self.team.pk, distinct_ids=["person1"], properties={"group": 1})
            person2 = person_factory(team_id=self.team.pk, distinct_ids=["person2"], properties={"group": 2})
            event2 = event_factory(
                team=self.team,
                distinct_id="person1",
                event="$pageview",
                properties={"$current_url": "https://something.com", "another_key": "value",},
            )
            event_factory(
                team=self.team,
                distinct_id="person2",
                event="$pageview",
                properties={"$current_url": "https://something.com"},
            )
            filter = Filter(
                data={
                    "properties": [
                        {"key": "group", "operator": "lt", "value": 2, "type": "person"},
                        {"key": "group", "operator": "gt", "value": 0, "type": "person"},
                    ]
                }
            )
            events = filter_events(filter=filter, team=self.team, person_query=True, order_by=None)
            self.assertEqual(events[0]["id"], event2.pk)
            self.assertEqual(len(events), 1)
        def test_boolean_filters(self):