Add test for packaging

Author: KitaitiMakoto

bindings/ruby/tests/test_package.rb

@@ -25,6 +25,8 @@ def test_install
       Dir.mktmpdir do |dir|
         system "gem", "install", "--install-dir", dir.shellescape, "--no-document", "pkg/#{filename.shellescape}", exception: true
         assert_path_exist File.join(dir, "gems/whispercpp-#{version}/lib", basename)
+        assert_path_exist File.join(dir, "gems/whispercpp-#{version}/LICENSE")
+        assert_path_not_exist File.join(dir, "gems/whispercpp-#{version}/ext/build")
       end
     end
   end