ext.tasks.Loop descriptor inheritance support

[lightmanLP]

Summary

Descriptor of disnake.ext.tasks.Loop returns new Loop instance instead of current class instance. Thats inheritance issue.

Checklist

• [x] If code changes were made, then they have been tested
  • [ ] I have updated the documentation to reflect the changes
  • [x] I have formatted the code properly by running pre-commit run --all-files
• [x] 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, ...)