allow for message in bits used event to be None

[jrutschke]

Description

For Twitch Combos Feature (currently in Beta: https://help.twitch.tv/s/article/combos?language=en_US) the message can be None.
ChannelBitsUse Event (event_bits_use) throws an error once Combos are redeemed.

Error before fix

twitchio/models/eventsub_.py", line 898, in __init__
    self.text: str | None = payload.get("message").get("text")
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get'

Example payload Combo: message is None

{'broadcaster_user_id': '63532168', 
'broadcaster_user_login': 'elspeth',
'broadcaster_user_name': 'Elspeth', 
'user_id': '70182062', 
'user_login': 'jacky_r', 
'user_name': 'Jacky_R', 
'bits': 5, 'type': 'combo', 
'power_up': None, 
'message': None
}

Example payload Cheer: message not None

{
'broadcaster_user_id': '63532168', 
'broadcaster_user_login': 'elspeth', 
'broadcaster_user_name': 'Elspeth', 
'user_id': '70182062', 
'user_login': 'jacky_r', 
'user_name': 'Jacky_R', 
'bits': 1, 
'type': 'cheer', 
'power_up': None, 
'message': {'text': 'Cheer1', 'fragments': [{'type': 'cheermote', 'text': 'Cheer1', 'cheermote': {'prefix': 'cheer', 'bits': 1, 'tier': 1}, 'emote': None}]}
}

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
  • I have updated the changelog with a quick recap of my changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)
• I have read and agree to the Developer Certificate of Origin for this contribution

[chillymosh]

In this case this should return None and not an empty string.
self.text: str = message.get("text") is sufficient.

This would be a breaking change otherwise for existing users checking explicitly for None and we do not need to accommodate a previous V1 instance.

[chillymosh]

Whilst correcting this, you can also update the docstring for fragments by removing
Is `None` if no chat message was used.

This was probably a copy paste error on my part.