Rollup merge of #128307 - ojeda:unescaped_backticks, r=GuillaumeGomez

Clean and enable `rustdoc::unescaped_backticks` for `core/alloc/std/test/proc_macro`

I am not sure if the lint is supposed to be "ready enough" (since it is `allow` by default), but it does catch a couple issues in `core` (`alloc`, `std`, `test` and `proc_macro` are already clean), so I propose making it `warn` in all the crates rendered in the website.

Cc: `@GuillaumeGomez`

library/core/src/slice/mod.rs

@@ -3435,8 +3435,8 @@ impl<T> [T] {
     /// elements of the slice move to the end while the last `k` elements move
     /// to the front.
     ///
-    /// After calling `rotate_right`, the element previously at index `self.len()
-    /// - k` will become the first element in the slice.
+    /// After calling `rotate_right`, the element previously at index
+    /// `self.len() - k` will become the first element in the slice.
     ///
     /// # Panics
     ///