don't run specs add at r64409 on Windows

Maybe it breaks 20180817T095734Z.fail.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64471 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/library/conditionvariable/wait_spec.rb

@@ -23,6 +23,7 @@ describe "ConditionVariable#wait" do
     th.join
   end
 
+  platform_is_not :windows do
   it "reacquires the lock even if the thread is killed" do
     m = Mutex.new
     cv = ConditionVariable.new
@@ -118,4 +119,5 @@ describe "ConditionVariable#wait" do
     cv.broadcast
     threads.each(&:join)
   end
+  end
 end