Don't show the A level change link when the course is withdrawn

app/decorators/course_decorator.rb

@@ -48,6 +48,8 @@ def open_or_closed_for_applications
   end
 
   def a_level_change_path
+    return if object.is_withdrawn?
+
     if object.a_level_subject_requirements.present?
       h.publish_provider_recruitment_cycle_course_a_levels_add_a_level_to_a_list_path(
         object.provider.provider_code,

spec/decorators/course_decorator_spec.rb

@@ -962,6 +962,20 @@
   describe '#a_level_change_path' do
     subject(:a_level_change_path) { course.decorate.a_level_change_path }
 
+    context 'when course is withdrawn' do
+      let(:course) do
+        build(
+          :course,
+          :with_a_level_requirements,
+          :withdrawn
+        )
+      end
+
+      it 'returns nil' do
+        expect(a_level_change_path).to be_nil
+      end
+    end
+
     context 'when course does not have an A level subject requirement' do
       let(:course) do
         build(