test: replace string concatenation with templates

PR-URL: nodejs/node#15903
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>

Author: cleong-tc

test/parallel/test-whatwg-url-parsing.js

@@ -36,7 +36,7 @@ for (const test of failureTests) {
         return false;
 
       // The input could be processed, so we don't do strict matching here
-      const match = (error + '').match(/Invalid URL: (.*)$/);
+      const match = (`${error}`).match(/Invalid URL: (.*)$/);
       if (!match) {
         return false;
       }