Enable nullable: System.Management.Automation.IModuleAssemblyInitializer (#14158)

src/System.Management.Automation/engine/Modules/ModuleIntrinsics.cs

@@ -1719,6 +1719,7 @@ namespace System.Management.Automation
     /// Used by Modules/Snapins to provide a hook to the engine for startup initialization
     /// w.r.t compiled assembly loading.
     /// </summary>
+#nullable enable
     public interface IModuleAssemblyInitializer
     {
         /// <summary>