Skip the spec on Windows because RUBY_EXE is RUNRUBY and it calls ruby as grandchild

spec/ruby/core/process/ppid_spec.rb

@@ -1,7 +1,9 @@
 require_relative '../../spec_helper'
 
 describe "Process.ppid" do
+  platform_is_not :windows do
     it "returns the process id of the parent of this process" do
       ruby_exe("puts Process.ppid").should == "#{Process.pid}\n"
     end
   end
+end