c9dbff2f42
Improve note for the `invalid_reference_casting` lint This PR add link to the book interior mutability chapter, https://doc.rust-lang.org/book/ch15-05-interior-mutability.html; this is done to guide peoples to a place with many useful information and context. *Note that this isn't the first occurrence of a link to the book in [tests outputs](https://github.com/search?q=repo%3Arust-lang%2Frust+book+path%3A%2F%5Etests%5C%2Fui%5C%2F%2F&type=code).* r? `@est31`