Update mdbook-spec to Rust 2024

Author: ehuss

mdbook-spec/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "mdbook-spec"
 version = "0.1.2"
-edition = "2021"
+edition = "2024"
 license = "MIT OR Apache-2.0"
 description = "An mdBook preprocessor to help with the Rust specification."
 repository = "https://github.com/rust-lang/spec/"