Create a user instead of stubbing one

To workaround https://gitlab.com/gitlab-org/gitlab-ee/issues/7144

ee/spec/services/projects/update_mirror_service_spec.rb

@@ -198,7 +198,7 @@ describe Projects::UpdateMirrorService do
       it "fails" do
         stub_fetch_mirror(project)
 
-        result = described_class.new(project, build_stubbed(:user)).execute
+        result = described_class.new(project, create(:user)).execute
 
         expect(result[:status]).to eq(:error)
       end