Rails 7.0 support

[willnet]

• Loose dependencies to allow Rails7 to be installed.
• Improved the CI setup to run tests with the latest Ruby and Rails.
  • jruby-head and ruby-2.2, ruby-2.1 with postgres fail, but I don't know how to fix it, so I leave it as it is.
  • fix tests due to Psych >= 4
  • add rubygems_mfa_required rubocop wants in gemspec
• CI result is here
  • This CI changed delayed_job dependencies to this branch temporarily to build successfully
  • because delayed_job master branch has a dependency with <= Rails 6.1 now
  • so This PR need to be merged after the PR merged.

[zavan]

Rails 7.0.1 supports Ruby 3.1 now. Should it be added to the matrix?

[willnet]

Added Ruby 3.1 and Rails 7.0.1 to ci settings 😃