nightly-2024-10-19: fix: Do not warn on unused self in traits (#6298)

# Description

## Problem\*

Resolves #6297 

## Summary\*

Sets `warn_if_unused` to `false` for the `self` parameter of a function
if it's for a trait implementation.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [ ] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.