Fix bundler error for Ruby 2.6 in CI

Author: brandoncc

test/abstract_unit.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
+# Only necessary as long as Ruby 2.6 compatibility is maintained
 require "rubygems" unless defined? Gem
+
 require "bundler/setup"
 
 lib = File.expand_path("#{File.dirname(__FILE__)}/../lib")