## 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/team.py
timezone: models.CharField = models.CharField(max_length=240, choices=TIMEZONES, default="UTC")
    data_attributes: models.JSONField = models.JSONField(default=get_default_data_attributes)
    
    plugins_opt_in: models.BooleanField = models.BooleanField(default=False)
    
    opt_out_capture: models.BooleanField = models.BooleanField(default=False)
    
    users: models.ManyToManyField = models.ManyToManyField(
        "User", blank=True, related_name="teams_deprecated_relationship"
    )
    
    event_names: models.JSONField = models.JSONField(default=list)
    event_names_with_usage: models.JSONField = models.JSONField(default=list)
    
    event_properties: models.JSONField = models.JSONField(default=list)
    event_properties_with_usage: models.JSONField = models.JSONField(default=list)
    event_properties_numerical: models.JSONField = models.JSONField(default=list)
    objects: TeamManager = TeamManager()
    def __str__(self):
        if self.name:
            return self.name
        if self.app_urls and self.app_urls[0]:
            return ", ".join(self.app_urls)
        return str(self.pk)
    __repr__ = sane_repr("uuid", "name", "api_token")
@receiver(models.signals.pre_delete, sender=Team)
def team_deleted(sender, instance, **kwargs):
    instance.event_set.all().delete()
    instance.elementgroup_set.all().delete()