Add GitHub Actions CI workflow

[r7kamura]

It seems that the TravisCI is no longer running, so I propose introducing a GitHub Actions workflow to run CI.

ATM, some issues are causing RSpec to fail. These should be resolved once the other pull requests I submitted are merged.

• Fix invalid dummy secret length for Rack::Session::Cookie in tests #171
• Add missing development dependency on rack-session #170
• Replace URI.escape with URI::DEFAULT_PARSER.escape #169

To stabilize CI runs, we changed the workflow to include Gemfile.lock in the Git repository. This helps avoid discrepancies between results when running locally versus in CI. While older Bundler templates typically did not include it, current templates do, making this approach generally considered the correct practice.

For the Ruby versions used in CI, I’ve decided to test against all currently maintained versions — that is, those that are not EOL and not preview releases — at the minor version level.
Going forward, I plan to enable deprecation warnings (and possibly treat them as errors) so that any issues arising with newer Ruby versions can be detected early.

There is evidence that an elaborate setup existed to run tests for each minor version of Rails, but I’ve removed it for now. The targeted versions are now quite old, and considering the current pace of development in this project, such an extensive testing setup seems unnecessary. If there’s a need to test these versions in the future, it can be addressed then.

RSpec has a mechanism to automatically detect whether the execution environment supports colored output. However, the GitHub Actions environment is somewhat special, and this detection can be incorrect. Therefore, we added the --force-color option here.

[r7kamura]

I was wondering — is this gem currently not being actively maintained due to a lack of maintainers?

Our company’s product has been using this gem for a long time, and we hope it will continue to be maintained in the future. I realize this might be presumptuous, but I’d be happy to help as a collaborator if you need an extra hand. Please let me know if there’s anything I can do to assist.