Currently, only JRuby 9.3 is covered by CI
- The compatibility docs state that JRuby 9.2 and 9.3 are covered, so 9.2 needs to be either added to CI or have its support dropped. (I think fine to drop support.)
- The latest release is 9.4.1.0 (see https://www.jruby.org/download). JRuby 9.4 was released Nov 23, 2022