Rename and allow `cast_ref_to_mut` lint This PR is a small subset of https://github.com/rust-lang/rust/pull/112431, that is the renaming of the lint (`cast_ref_to_mut` -> `invalid_reference_casting`). BUT also temporarily change the default level of the lint from deny-by-default to allow-by-default until https://github.com/rust-lang/rust/pull/112431 is merged. r? `@Nilstrieb`