futures-util: Allow missing_debug_implementations on WakerToHandle

[zjijz]

Fixes this error on ToT:

error: type does not implement `Debug`; consider adding `#[derive(Debug)]` or a manual implementation
   --> futures-util/src/compat/compat01as03.rs:325:1
    |
325 | struct WakerToHandle<'a>(&'a task03::Waker);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D missing-debug-implementations` implied by `-D warnings`

Tested:

• cargo fmt.
• cargo doc.
• cargo test --all-features.

[taiki-e]

Thanks for the PR. This is rustc bug (rust-lang/rust#111359), so I prefer to use #[allow(...)] with a link to the bug report rather than follow the buggy lint.

[zjijz]

Changed the fix to use #[allow(missing_debug_implementations)] and added a link to the above issue. Let me know if it's good to go!

[taiki-e]

The rustc commit that caused the issue has been reverted and this issue is now fixed as well, so I'm going to close this.

Thanks for the PR anyway.