Environment Information

Error occurred in Github Actions: https://github.com/jeremyevans/ruby-cicphash/actions/runs/3544830713/jobs/5952456756
jruby 9.4.0.0 (3.1.0) 2022-11-23 95c0ec159f OpenJDK 64-Bit Server VM 11.0.17+8 on 11.0.17+8 +jit [x86_64-linux]

Expected Behavior

JRuby 9.4 should define the same public instance methods for Hash that Ruby 3.1 defines.

Actual Behavior

JRuby 9.4 defines Hash#index, was was removed in Ruby 3.0.

JRuby 9.4 defines ruby2_keywords_hash and ruby2_keywords_hash? as Hash instance methods, when they should be defined as Hash class methods.