Clippy suggestion about borrowed_box when trait object is boxed is incomplete

Summary

This follows from https://github.com/rust-lang/rust-clippy/issues/3971
and https://github.com/rust-lang/rust-clippy/issues/8161.

I think the message should suggest the .as_ref() method at the call site.

Reproducer

Clippy reported this:

warning: you seem to be trying to use `&Box<T>`. Consider using just `&T`
  --> advent2023-bin/src/main.rs:46:54
   |
46 |     let get_result_pair = move |day_num: usize, day: &Box<dyn DayTrait>| -> (String, String) {
   |                                                      ^^^^^^^^^^^^^^^^^^ help: try: `&dyn DayTrait`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#borrowed_box
   = note: `#[warn(clippy::borrowed_box)]` on by default

When fixed as indicated:

error[E0277]: the trait bound `Box<dyn DayTrait>: DayTrait` is not satisfied
  --> advent2023-bin/src/main.rs:63:76
   |
63 |             print_day(day_num, day.get_display(), get_result_pair(day_num, &day));
   |                                                                            ^^^^ the trait `DayTrait` is not implemented for `Box<dyn DayTrait>`
   |
   = help: the trait `DayTrait` is implemented for `Day<D, O, C, F, S>`
   = note: required for the cast from `&Box<dyn DayTrait>` to `&dyn DayTrait`

See minimum reproduction:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=88aa6d38369c9c8f48eabf5899ed65b0

Version

rustc 1.76.0-nightly (87e1447aa 2023-11-30)
binary: rustc
commit-hash: 87e1447aadaa2899ff6ccabe1fa669eb50fb60a1
commit-date: 2023-11-30
host: x86_64-unknown-linux-gnu
release: 1.76.0-nightly
LLVM version: 17.0.5

Additional Labels

No response

Start with the linked Rust Playground minimum reproduction and locate the borrowed_box lint in rust-clippy. Confirm the diagnostic for the boxed trait object, then update the lint’s test coverage so the call-site suggestion includes .as_ref().