[user_activity] TypeError: string indices must be integers

[sentry]

Sentry Issue: BUGBOT-ZT

TypeError: string indices must be integers
(10 additional frame(s) were not displayed)
...
  File "bugbot/bzcleaner.py", line 796, in send_email
    email_data = self.get_email_data(date)
  File "bugbot/bzcleaner.py", line 712, in get_email_data
    bugs = self.get_bugs(date=date)
  File "bugbot/rules/needinfo_regression_author.py", line 178, in get_bugs
    bugs = self.filter_bugs(bugs)
  File "bugbot/rules/needinfo_regression_author.py", line 148, in filter_bugs
    users_info = UserActivity(include_fields=["groups", "requests"]).check_users(
  File "bugbot/user_activity.py", line 168, in check_users
    ).wait()

Rule needinfo_regression_author