Fix typo in voice_client.py

[HigherOrderLogic]

Warning: We have a feature freeze till release

That means we won't accept new features for now. Only bug fixes.

Summary

Fix small typo for doc in voice_client.py

Checklist

• 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
• 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, ...)