Fix for missing self.name/self.description in SlashCommandGroup

[krittick]

Summary

This adds self.name and self.description to SlashCommandGroup which are needed as of commit 67f1e13 (though I'm not entirely sure why).

Closes #675

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, ...)

[Lulalaby]

Interesting