use the proper property name in specified_values tests

We used a string instead of stringify!'ing the name, whoops.

tests/unit/stylo/specified_values.rs

@@ -17,7 +17,7 @@ fn size_of_specified_values() {
                 let size = size_of::<style::properties::longhands::$name::SpecifiedValue>();
                 let is_boxed = $boxed;
                 if (!is_boxed && size > threshold) || (is_boxed && size <= threshold) {
-                    bad_properties.push(("$name", size, is_boxed));
+                    bad_properties.push((stringify!($name), size, is_boxed));
                 }
             )+
         }