[rubygems/rubygems] Suppress warnings coming from jar-dependencies

This is a default gem on jruby, which ships with a rubygems plugin,
which prints warnings all over the place during our tests.

This plugin is unnecessary from our tests, so I disable it through the
`JARS_SKIP` environment variable provided by this gem.

0aabbcf269

lib/rubygems/test_case.rb

@@ -30,6 +30,8 @@ require 'bundler'
 
 require 'minitest/autorun'
 
+ENV["JARS_SKIP"] = "true" if Gem.java_platform? # avoid unnecessary and noisy `jar-dependencies` post install hook
+
 require 'rubygems/deprecate'
 
 require 'fileutils'