[ext.commands] Fix non-async method in owner_or_permission doc example

[krittick]

Summary

This updates the ext.commands documentation to make the owner_or_permissions example asynchronous, as it would currently fail if used as-is due to the presence of an async call in the function.

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, ...)