Docs: Update ambiguous for...in example for guard-for-in (#10114)

Author: w3cj

docs/rules/guard-for-in.md

@@ -33,6 +33,9 @@ for (key in foo) {
     if (Object.prototype.hasOwnProperty.call(foo, key)) {
         doSomething(key);
     }
+}
+
+for (key in foo) {
     if ({}.hasOwnProperty.call(foo, key)) {
         doSomething(key);
     }