update: actions/checkout@v4

[ksaito422]

Due to the end of support for Node.js 16, I would like to update the actions to use Node.js 20.

see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

[ksaito422]

@mame A warning has been introduced in ruby/ruby#10428, indicating that ostruct will become a bundled gem starting from Ruby 3.5.

Upon checking the CI error logs, I saw this warning and added the dependency to the gemspec:

output from parser-cmd (stderr):
  /opt/hostedtoolcache/Ruby/3.3.5/x64/lib/ruby/3.3.0/json/common.rb:3: warning: ostruct was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
  You can add ostruct to your Gemfile or gemspec to silence this warning.

After making this change, the CI passed successfully, so I believe this resolves the necessary updates for GitHub Actions.

I would appreciate it if you could review the changes again. Thank you for your time 🙏

[mame]

@ksaito422 Thank you for the PR, but please do not add a dependency to ostruct. The perfect_toml gem itself does not depend on the ostruct gem. Only the test script does. I guess adding gem "json", ">= 2.7.2" to Gemfile will solve the issue.

[ksaito422]

@ksaito422 Thank you for the PR, but please do not add a dependency to ostruct. The perfect_toml gem itself does not depend on the ostruct gem. Only the test script does. I guess adding gem "json", ">= 2.7.2" to Gemfile will solve the issue.

Thanks for the advice. I had overlooked the dependency there.
I have addressed it, please check.

[mame]

Thanks!