test(rustfix): Update for nightly

Inspired by #15713

Author: epage

crates/rustfix/tests/everything/dedup-suggestions.fixed.rs

@@ -1,7 +1,8 @@
 // See <https://github.com/rust-lang/cargo/issues/13027>
 macro_rules! foo {
     () => {
-        let _ = &1;
+        let x = Box::new(1);
+        let _ = &x;
     };
 }