test: advance clock past live region fade before final snapshot

Author: isherstneva

__tests__/html2/accessibility/sendBox/alertEmptyMessage.singleLineTextBox.enter.html

@@ -72,6 +72,9 @@
 
         // THEN: Both error and status messages should be empty.
         expect(errorMessage.innerText).toBe('');
+
+        // THEN: After live region fade, the live region should be empty.
+        clock.tick(10000);
         await host.snapshot('local');
       });
     </script>