fixed nested form file upload spec

Author: jonasjabari

spec/test/components/dynamic/form/nested_forms_spec.rb

@@ -1380,8 +1380,8 @@ def form_config
         expect(DummyChildModel.find(id_of_child_0).files[0].blob.filename).to eq("matestack-logo.png")
         expect(DummyChildModel.find(id_of_child_0).files[1].blob.filename).to eq("corgi.mp4")
 
-        expect(DummyChildModel.find(id_of_child_1).file.nil? || DummyChildModel.find(id_of_child_1).file&.blob&.nil?).to be true
-        expect(DummyChildModel.find(id_of_child_1).files.empty?).to be true
+        expect(DummyChildModel.find(id_of_child_1).file.attached?).to be false
+        expect(DummyChildModel.find(id_of_child_1).files.attached?).to be false
 
         expect(DummyChildModel.find(id_of_child_2).file.blob.filename).to eq("corgi.mp4")
         expect(DummyChildModel.find(id_of_child_2).files[0].blob.filename).to eq("matestack-logo.png")