fix: deprecated use of dict methods on _PayloadLike classes

[Revnoplex]

Caution

Feature freeze is active, as described by our Release Schedule.

Summary

Found deprecated use of dict operations on the _PayloadLike class RawVoiceStateUpdateEvent that emitted the following deprecation warning:

.venv/lib/python3.13/site-packages/discord/voice/state.py:349: DeprecationWarning: __getitem__ is deprecated since version 2.7 and will be removed in version 3.0. Consider using the attributes instead.
  self.session_id = data["session_id"]

This pr replaces it with the attribute data.session_id instead.
I traced usages of RawVoiceStateUpdateEvent and the other _PayloadLike class RawVoiceServerUpdateEvent with my IDE, but found no other usages of dict operations with them. But feel free to double check as I don't trust myself with my IDE's search functions

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]

Thanks for opening this pull request!
Please make sure you have read the Contributing Guidelines and Code of Conduct.

This pull request can be checked-out with:

git fetch origin pull/3189/head:pr-3189
git checkout pr-3189

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3189/head

[Revnoplex]

ah the unresponsive pre-commit check caused a styling issue to slip through and cause the pre-commit check to fail on master

[Revnoplex]

doesn't matter now, it fixed the styling in the other pr when I updated it that just got merged