Skip tests that depend on native structuredClone() if not available

The polyfill isn't 100% precise

Author: amezin

spec/core/SpecSpec.js

@@ -114,6 +114,10 @@ describe('Spec', function() {
     });
 
     it('throws if the value is not structured-cloneable', function() {
+      if (typeof structuredClone === 'undefined') {
+        pending('This test requires native structuredClone');
+      }
+
       const spec = new privateUnderTest.Spec({
         queueableFn: { fn: () => {} }
       });

spec/core/SuiteSpec.js

@@ -416,6 +416,10 @@ describe('Suite', function() {
     });
 
     it('throws if the value is not structured-cloneable', function() {
+      if (typeof structuredClone === 'undefined') {
+        pending('This test requires native structuredClone');
+      }
+
       const suite = new privateUnderTest.Suite({});
 
       expect(function() {