Add module initializer for Verify.SourceGenerators (dotnet#60547)

Author: captainsafia

src/Http/Http.Extensions/test/ModuleInitializer.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+
+public static class ModuleInitializer
+{
+    [ModuleInitializer]
+    public static void Init() =>
+        VerifySourceGenerators.Initialize();
+}