Fix warning on duplicate test ignore attribute

    warning: unused attribute
      --> tests/test_size.rs:27:60
       |
    27 | #[cfg_attr(not(all(wrap_proc_macro, not(span_locations))), ignore)]
       |                                                            ^^^^^^
       |
       = note: #[warn(unused_attributes)] on by default

tests/test_size.rs

@@ -24,7 +24,7 @@ fn test_proc_macro2_fallback_span_size_with_locations() {
 }
 
 #[rustversion::attr(before(1.32), ignore)]
-#[cfg_attr(not(all(wrap_proc_macro, not(span_locations))), ignore)]
+#[rustversion::attr(since(1.32), cfg_attr(not(all(wrap_proc_macro, not(span_locations))), ignore))]
 #[test]
 fn test_proc_macro2_wrapper_span_size_without_locations() {
     assert_eq!(mem::size_of::<proc_macro2::Span>(), 4);