Stop running CI against JRuby and some CI config cleanup

[st0012]

Due to mkristian/jar-dependencies#86, the JRuby CI hasn't been running for a while.

bundler: failed to load command: rake (/Users/runner/work/rdoc/rdoc/vendor/bundle/jruby/3.1.0/bin/rake)
Gem::LoadError: You have already activated jar-dependencies 0.5.0, but your Gemfile requires jar-dependencies 0.4.1. Since jar-dependencies is a default gem, you can either remove your dependency on it or try updating to a newer version of bundler that supports jar-dependencies as a default gem.
  check_for_activated_spec! at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/runtime.rb:30[8](https://github.com/ruby/rdoc/actions/runs/12235162661/job/34125882061#step:6:9)
                      setup at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/runtime.rb:25
                       each at org/jruby/RubyArray.java:2009
                       each at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/spec_set.rb:155
                        map at org/jruby/RubyEnumerable.java:818
                      setup at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/runtime.rb:24
                      setup at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler.rb:161
                     <main> at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/setup.rb:20
                 with_level at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/ui/shell.rb:136
                    silence at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/ui/shell.rb:88
                     <main> at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/setup.rb:20
                    require at org/jruby/RubyKernel.java:1187
           require_relative at org/jruby/RubyKernel.java:1216
                kernel_load at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/cli/exec.rb:56
                        run at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/cli/exec.rb:23
                       exec at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/cli.rb:486
                        run at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/vendor/thor/lib/thor/command.rb:27
             invoke_command at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/vendor/thor/lib/thor/invocation.rb:127
                   dispatch at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/vendor/thor/lib/thor.rb:3[9](https://github.com/ruby/rdoc/actions/runs/12235162661/job/34125882061#step:6:10)2
                   dispatch at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/cli.rb:31
                      start at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/vendor/thor/lib/thor/base.rb:485
                      start at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/cli.rb:25
                     <main> at /Users/runner/.rubies/jruby-head/lib/ruby/gems/shared/gems/bundler-2.3.26/exe/bundle:48
       with_friendly_errors at /Users/runner/.rubies/jruby-head/lib/ruby/stdlib/bundler/friendly_errors.rb:[12](https://github.com/ruby/rdoc/actions/runs/12235162661/job/34125882061#step:6:13)0
                     <main> at /Users/runner/.rubies/jruby-head/lib/ruby/gems/shared/gems/bundler-2.3.26/exe/bundle:36
                       load at org/jruby/RubyKernel.java:1223
                     <main> at /Users/runner/.rubies/jruby-head/bin/bundle:25

@headius feel free to add JRuby back once the jar-dependencies issue has been resolved.

[headius]

@st0012 I would have appreciated a separate bug report about this. The error that appears in the jobs here is not related to the version conflict issue that you linked (some undefined method 'each' while trying to lock the jar files).

I will look into that issue.

[headius]

This should be fixed by mkristian/jar-dependencies@df35d52. I'll do another PR to reenable.

[headius]

Once the jruby-head builds installed by setup-ruby get updated (overnight tonight or tomorrow) then this should be fixed by #1229. I did not exclude Windows for now to see if it is passing (don't know why it wouldn't be).