feat(curriculum): use correct terms skyline project step 4 (freeCodeCamp#55871)

Author: a2937

curriculum/challenges/english/14-responsive-web-design-22/learn-css-variables-by-building-a-city-skyline/5d822fd413a79914d39e98cc.md

@@ -63,7 +63,7 @@ const heads = document.querySelectorAll('head');
 assert.equal(heads?.length, 1);
 ```
 
-You should have one self-closing `link` element.
+You should have one void `link` element.
 
 ```js
 assert(document.querySelectorAll('link').length === 1);