HypeTrain return empty shared_train_participants list if not shared_train

[jrutschke]

Description

Small fix to fix to resolve TypeError for all hype train events. If not a shared train, return empty list for shared_train_participants.
Problem in BaseHypeTrain causes the same error for hype train begin, progress and end due to 'shared_train_participants' in event being None.

File "/twitchio/models/eventsub_.py", line 4960, in __init__
    self.shared_train_participants: list[PartialUser] = [
                                                        ^
TypeError: 'NoneType' object is not iterable

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]

LGTM

[EvieePy]

Did you ever verify if this fixes your issue? If not I can look into it for you.

[jrutschke]

Unfortunately no new Hype Train Event since then. Hopefully this weekend latest.

[jrutschke]

Finally verified! Ready to merge.