Steps to Reproduce

1. Run group member bot from examples
2. Start the bot
3. Error async def track_chats(update: Update, context: CallbackContext.DEFAULT_TYPE) -> None: AttributeError: type object 'CallbackContext' has no attribute 'DEFAULT_TYPE'

Expected behaviour

Should run as in previous -pre without issues

Actual behaviour

Error and exit

Operating System

linux

Version of Python, python-telegram-bot & dependencies

: python-telegram-bot
Version: 20.0a1
Summary: We have made you a wrapper you can't refuse
Home-page: https://python-telegram-bot.org/
Author: Leandro Toledo
Author-email: devs@python-telegram-bot.org
License: LGPLv3
Location: /home/alarm/dev/bots/unit/professor-moon-home/venv/lib/python3.10/site-packages
Requires: APScheduler, cachetools, httpx, pytz, tornado
Required-by: 

Python 3.10.5

Relevant log output

No response

Additional Context

No response