Enforce trailing comma in JS on multiline (#30002)

To keep blame info accurate and to avoid [changes like
this](https://github.com/go-gitea/gitea/pull/29977/files#diff-c3422631a14edbe1e508c4b22f0c718db318be08a6e889427802f9b6165d88d6R359),
it's good to always have a trailing comma, so let's enforce it in JS.

This rule is completely automatically fixable with `make lint-js-fix`
and that's what I did here.

web_src/js/webcomponents/polyfills.js

@@ -9,7 +9,7 @@ try {
       return {
         format(value) {
           return ` ${value} ${options.unit}`;
-        }
+        },
       };
     }
     return intlNumberFormat(locales, options);