Auto merge of #124112 - beetrees:incremental-os-str, r=Nadrieril

Fix ICE when there is a non-Unicode entry in the incremental crate directory

Fix the ICE that occurs when there is a non-Unicode entry in the incremental crate directory by replacing uses of `to_string_lossy` + `assert_no_characters_lost` with `to_str`. The added test would cause the compiler to ICE before this PR.