Update test assertions when default policy moves an attribute during Attr.value like setters

The draft spec PR now early returns in the case the element of the attribute changes rather than updating the value.

See whatwg/dom#1268

Author: lukewarlow

Diff for: trusted-types/set-attributes-mutations-in-callback.tentative.html

@@ -192,16 +192,16 @@
         case "Attr.value":
         case "Node.nodeValue":
         case "Node.textContent":
-          // These APIs successfully sets the attribute node value, the default
-          // policy's callback moved that node on the other element.
+          // These APIs early return when the element changes, but the default policy's
+          // callback still sets the attribute on the other element.
           returnValue = setterData.runSetter(element, testData.attrNS,
                                              testData.attrName,
                                              input_string, testData.type);
           assert_equals(element.attributes.length, 0);
           assert_equals(otherElement.attributes.length, 1);
           assert_equals(otherElement.getAttributeNS(testData.attrNS,
                                                   testData.attrName),
-                        output_string);
+                        other_string);
           break;
         default:
           assert_unreached();