Always use --apply-cop-headers in ThreadingAppTest

Author: halter73

src/Components/test/E2ETest/Infrastructure/ServerFixtures/BlazorWasmTestAppFixture.cs

@@ -25,6 +25,8 @@ public class BlazorWasmTestAppFixture<TProgram> : WebHostServerFixture
     public string PathBase { get; set; }
     public string ContentRoot { get; private set; }
 
+    public bool RequiresMultithreadingHeaders { get; set; }
+
     protected override IHost CreateWebHost()
     {
         if (TestTrimmedOrMultithreadingApps)
@@ -61,7 +63,7 @@ protected override IHost CreateWebHost()
             args.Add(Environment);
         }
 
-        if (WebAssemblyTestHelper.MultithreadingIsEnabled())
+        if (RequiresMultithreadingHeaders || WebAssemblyTestHelper.MultithreadingIsEnabled())
         {
             args.Add("--apply-cop-headers");
         }

src/Components/test/E2ETest/Tests/ThreadingAppTest.cs

@@ -19,6 +19,7 @@ public ThreadingAppTest(
         ITestOutputHelper output)
         : base(browserFixture, serverFixture, output)
     {
+        serverFixture.RequiresMultithreadingHeaders = true;
     }
 
     protected override void InitializeAsyncCore()