Ensure CI is using jruby 9.4.13.0

In the original work for upgrading to jruby 9.4.13.0 we missed upgrading the packaged version of ruby on CI runners for integration tests etc. See https://github.com/elastic/logstash/pull/16642 as an example of another upgrade. This will involve making a change to ci-agent-images (see https://github.com/search?q=repo%3Aelastic%2Fci-agent-images%209.4.9.0&type=code for inspiration). 