A small diagnostic improvement for dropping_copy_types For a value `m` which implements `Copy` trait, `drop(m);` does nothing. We now suggest user to ignore it by a abstract and general note: `let _ = ...`. I think we can give a clearer note here: `let _ = m;` fixes #125189 <!-- If this PR is related to an unstable feature or an otherwise tracked effort, please link to the relevant tracking issue here. If you don't know of a related tracking issue or there are none, feel free to ignore this. This PR will get automatically assigned to a reviewer. In case you would like a specific user to review your work, you can assign it to them by using r​? <reviewer name> -->