Use --web-server-use-cop.

Author: maraf

src/libraries/System.Private.Runtime.InteropServices.JavaScript/tests/System.Private.Runtime.InteropServices.JavaScript.Tests.csproj

@@ -3,7 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Browser</TargetFrameworks>
     <TestRuntime>true</TestRuntime>
-    <WasmXHarnessArgs>$(WasmXHarnessArgs) --engine-arg=--expose-gc</WasmXHarnessArgs>
+    <WasmXHarnessArgs>$(WasmXHarnessArgs) --engine-arg=--expose-gc --web-server-use-cop</WasmXHarnessArgs>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Runtime\InteropServices\JavaScript\JavaScriptTests.cs" />