Rollup merge of #140348 - ehuss:lint-docs-edition, r=compiler-errors

Update lint-docs to default to Rust 2024

This updates the lint-docs tool to default to the 2024 edition. The lint docs are supposed to illustrate the code with the latest edition, and I just forgot to update this in https://github.com/rust-lang/rust/pull/133349.

Some docs needed to add the `edition` attribute since they were assuming a particular edition, but were missing the explicit annotation.

This also includes a commit to simplify the edition handling in lint-docs.

compiler/rustc_lint/src/builtin.rs

@@ -948,7 +948,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// #[no_mangle]
     /// const FOO: i32 = 5;
     /// ```

compiler/rustc_lint/src/impl_trait_overcaptures.rs

@@ -41,7 +41,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// # #![deny(impl_trait_overcaptures)]
     /// # use std::fmt::Display;
     /// let mut x = vec![];

compiler/rustc_lint_defs/src/builtin.rs

@@ -1424,7 +1424,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// macro_rules! foo {
     ///    () => {};
     ///    ($name) => { };
@@ -4128,7 +4128,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,compile_fail
+    /// ```rust,compile_fail,edition2021
     /// #![deny(dependency_on_unit_never_type_fallback)]
     /// fn main() {
     ///     if true {