Add JRuby 9.4 to testing matrix; nerf ActiveJob::TestQueueAdapter overrides

[bensheldon]

I am experiencing problems with JRuby 9.4.3.0 and the usage of prepend and calling descendants (which is called by ActiveJob::TestHelper, with exceptions that look like: jruby/jruby#6896

It is a little strange though because it could be a combination of stub_constant and doing weird things with ActiveSupport::Concern like:

good_job/lib/good_job/active_job_extensions/concurrency.rb

Lines 23 to 24 in d1cde17

	included do
	prepend Prepends

Unfortunately, I wasn't able to isolate it down, but my working theory is that something like this should be problematic (though maybe it is specifically stub_const):

require 'bundler/inline'
gemfile do
  gem 'activesupport'
end

require 'active_support/concern'
require 'active_support/descendants_tracker'
module Paws
  extend ::ActiveSupport::Concern

  module Prepends
    def paws
      puts 'PAWS'
    end
  end

  included do
    prepend Prepends
  end
end

class Animal
  extend ActiveSupport::DescendantsTracker
end

class Dog < Animal
  include Paws
end

puts Dog.new.paws
puts Animal.descendants
puts ObjectSpace.each_object(Module).each(&:singleton_class)