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/std/src/lib.rs

@@ -254,6 +254,7 @@
 #![deny(fuzzy_provenance_casts)]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![allow(rustdoc::redundant_explicit_links)]
+#![warn(rustdoc::unescaped_backticks)]
 // Ensure that std can be linked against panic_abort despite compiled with `-C panic=unwind`
 #![deny(ffi_unwind_calls)]
 // std may use features in a platform-specific way