Add a project spec

Follow up rubocop/rubocop#12319

spec/project_spec.rb

@@ -260,6 +260,10 @@
 
       dir = File.expand_path('../changelog', __dir__)
 
+      it 'will not have a directory' do
+        expect(Dir["#{dir}/*"].none? { |path| File.directory?(path) }).to be(true)
+      end
+
       Dir["#{dir}/*.md"].each do |path|
         context "For #{path}" do
           let(:path) { path }