Automatically validate full Rails 8.0 and 8.1 support

[chadlwilson]

• add Rails 8.0 regression test for 10.0 and 10.1
• "Full" Rails 8.1 and Rack 3.x support
  • Rack 3.x / Rails 8.1 support jruby-rack#304
  • Release of jruby-rack 1.3.x or 2.1.x