Test against RedMica 3.0.1 and Ruby 3.3

[hidakatsuya]

This PR includes the following changes:

• Change the test target to RedMica 3.0.1 and Ruby 3.3
• Add a temporary workaround to avoid test failures due to the change from unprocessable_entity to unprocessable_content in Rack 3.1.0
  • In Rack 3.1.0 and later, all tests to verify that the response code is :unprocesable_entity fail. More info: https://github.com/hidakatsuya/redmica_ui_extension/actions/runs/9756212264/job/26926081378
  • This has been resolved in the Redmine master branch, but not yet in RedMica.

[ishikawa999]

The test at https://github.com/redmica/redmica_ui_extension/actions/runs/9950777857/job/27494635499 has failed, but I think this is due to factors other than the CI configuration. I have merged it, thank you.