Warn on rustdoc::unescaped_backticks for core and alloc

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

library/alloc/src/lib.rs

@@ -86,6 +86,7 @@
 #![warn(multiple_supertrait_upcastable)]
 #![allow(internal_features)]
 #![allow(rustdoc::redundant_explicit_links)]
+#![warn(rustdoc::unescaped_backticks)]
 #![deny(ffi_unwind_calls)]
 //
 // Library features:

library/core/src/lib.rs

@@ -103,6 +103,7 @@
 #![deny(ffi_unwind_calls)]
 // Do not check link redundancy on bootstraping phase
 #![allow(rustdoc::redundant_explicit_links)]
+#![warn(rustdoc::unescaped_backticks)]
 //
 // Library features:
 // tidy-alphabetical-start