fix: Fix parsing of SOUNDBOARD_SOUNDS gateway event

[Paillat-dev]

Summary

No changelog this time since technically we never provided a public way of requesting that event in the first place, so the issue could never happen in practice. It is nonetheless present when testing.

This bug was identified by Anthropic Claude Opus 4.8, then verified and patched by me.

Information

• 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, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.
• AI Usage has been disclosed.
  • If AI has been used, I understand fully what the code does

[pycord-app]

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This pull request can be checked-out with:

git fetch origin pull/3264/head:pr-3264
git checkout pr-3264

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3264/head