Combine ObjectStorage spec contexts

`uploaders/object_storage_spec.rb` previously had two `context` blocks
on the same tree level that are both labelled 'when local file is used':

https://gitlab.com/gitlab-org/gitlab/-/blob/44002f46888a5944c710a04a016f6fa3ef45e466/spec/uploaders/object_storage_spec.rb#L599
https://gitlab.com/gitlab-org/gitlab/-/blob/44002f46888a5944c710a04a016f6fa3ef45e466/spec/uploaders/object_storage_spec.rb#L615

After asking in this issue:

https://gitlab.com/gitlab-org/gitlab/-/issues/209967

The decision was to combine them.

spec/uploaders/object_storage_spec.rb

@@ -596,22 +596,6 @@ describe ObjectStorage do
       uploader.cache!(uploaded_file)
     end
 
-    context 'when local file is used' do
-      context 'when valid file is used' do
-        let(:uploaded_file) do
-          fixture_file_upload('spec/fixtures/rails_sample.jpg', 'image/jpg')
-        end
-
-        it "properly caches the file" do
-          subject
-
-          expect(uploader).to be_exists
-          expect(uploader.path).to start_with(uploader_class.root)
-          expect(uploader.filename).to eq('rails_sample.jpg')
-        end
-      end
-    end
-
     context 'when local file is used' do
       let(:temp_file) { Tempfile.new("test") }
 
@@ -627,6 +611,14 @@ describe ObjectStorage do
         context 'when valid file is specified' do
           let(:uploaded_file) { temp_file }
 
+          it 'properly caches the file' do
+            subject
+
+            expect(uploader).to be_exists
+            expect(uploader.path).to start_with(uploader_class.root)
+            expect(uploader.filename).to eq(File.basename(uploaded_file.path))
+          end
+
           context 'when object storage and direct upload is specified' do
             before do
               stub_uploads_object_storage(uploader_class, enabled: true, direct_upload: true)