Auto merge of #5480 - sinkuu:unit_arg_app, r=flip1995
Auto merge of #5480 - sinkuu:unit_arg_app, r=flip1995

unit_arg suggestion is not really machine-applicable

This lint suggests replacing any code returining `()`-type with `()` literal, which can change the behavior. e.g. `Ok(do_something())` -> `OK(())`.

---

changelog: none

graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust