[rubygems/rubygems] Get specs to run on JRuby and make them pass

Turns out we were not running specs on JRuby, so we introduced a
failure. Seems fine to skip.

https://github.com/rubygems/rubygems/commit/4e2d6affb3

spec/bundler/install/gemfile/force_ruby_platform_spec.rb

@@ -102,6 +102,8 @@ RSpec.describe "bundle install with force_ruby_platform DSL option", :jruby do
     end
 
     it "reinstalls the ruby variant when a platform specific variant is already installed, the lockile has only ruby platform, and :force_ruby_platform is used in the Gemfile" do
+      skip "Can't simulate platform reliably on JRuby, installing a platform specific gem fails to activate io-wait because only the -java version is present, and we're simulating a different platform" if RUBY_ENGINE == "jruby"
+
       lockfile <<-L
         GEM
           remote: https://gem.repo4

spec/bundler/realworld/fixtures/warbler/Gemfile

@@ -3,5 +3,5 @@
 source "https://rubygems.org"
 
 gem "demo", path: "./demo"
-gem "jruby-jars", "~> 9.2"
+gem "jruby-jars", "~> 9.4"
 gem "warbler", "~> 2.0"

spec/bundler/realworld/fixtures/warbler/Gemfile.lock

@@ -6,7 +6,7 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    jruby-jars (9.2.16.0)
+    jruby-jars (9.4.8.0)
     jruby-rack (1.1.21)
     rake (13.0.1)
     rubyzip (1.3.0)
@@ -23,8 +23,8 @@ PLATFORMS
 
 DEPENDENCIES
   demo!
-  jruby-jars (~> 9.2)
+  jruby-jars (~> 9.4)
   warbler (~> 2.0)
 
 BUNDLED WITH
-   2.5.0.dev
+   2.6.0.dev