Add "not guaranteed to be equal"

Co-authored-by: Urgau <3616612+Urgau@users.noreply.github.com>

library/core/src/ptr/mod.rs

@@ -2180,7 +2180,7 @@ pub fn addr_eq<T: ?Sized, U: ?Sized>(p: *const T, q: *const U) -> bool {
 ///   let f: fn(i32) -> i32 = |x| x;
 ///   let g: fn(i32) -> i32 = |x| x + 0;  // different closure, different body
 ///   let h: fn(u32) -> u32 = |x| x + 0;  // different signature too
-///   dbg!(std::ptr::fn_addr_eq(f, g), std::ptr::fn_addr_eq(f, h));
+///   dbg!(std::ptr::fn_addr_eq(f, g), std::ptr::fn_addr_eq(f, h)); // not guaranteed to be equal
 ///   ```
 ///
 /// * May return `false` in any case.