Additional namespace validation for AdditionalPack

When changing the namespace for Ci::Minutes::AdditionalPacks
we should ensure the namespaces are not the same (unneccessary)

Changelog: other
EE: true

ee/app/services/ci/minutes/additional_packs/change_namespace_service.rb

@@ -46,6 +46,7 @@ module Ci
           raise ChangeNamespaceError, 'Target namespace must be provided' unless target.present?
           raise ChangeNamespaceError, 'Namespace must be a top-level namespace' unless namespace.root?
           raise ChangeNamespaceError, 'Target namespace must be a top-level namespace' unless target.root?
+          raise ChangeNamespaceError, 'Namespace and target must be different' if namespace == target
         end
 
         def validate_owners!

ee/spec/services/ci/minutes/additional_packs/change_namespace_service_spec.rb

@@ -111,6 +111,15 @@ RSpec.describe Ci::Minutes::AdditionalPacks::ChangeNamespaceService do
           expect(change_namespace[:message]).to eq 'Both namespaces must share the same owner'
         end
       end
+
+      context 'when the namespace is the same as the target' do
+        let(:target) { namespace }
+
+        it 'returns an error' do
+          expect(change_namespace[:status]).to eq :error
+          expect(change_namespace[:message]).to eq 'Namespace and target must be different'
+        end
+      end
     end
   end
 end