Fix order-dependent spec failure in appearance_spec.rb

When file_mover_spec.rb ran, it would initialize fog-aws with
`Fog::AWS::Storage::Real` service instead of `Fog::AWS::Storage::Mock`
because `Fog.mock!` was not called. Ensure that we use
`stub_uploads_object_storage` to prevent that from happening.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64083

spec/models/appearance_spec.rb

@@ -21,7 +21,7 @@ describe Appearance do
     end
   end
 
-  context 'with uploads', :quarantine do
+  context 'with uploads' do
     it_behaves_like 'model with uploads', false do
       let(:model_object) { create(:appearance, :with_logo) }
       let(:upload_attribute) { :logo }

spec/uploaders/file_mover_spec.rb

@@ -85,8 +85,7 @@ describe FileMover do
 
     context 'when tmp uploader is not local storage' do
       before do
-        allow(PersonalFileUploader).to receive(:object_store_enabled?) { true }
-        tmp_uploader.object_store = ObjectStorage::Store::REMOTE
+        stub_uploads_object_storage(uploader: PersonalFileUploader)
         allow_any_instance_of(PersonalFileUploader).to receive(:file_storage?) { false }
       end