drbtest.rb: avoid leaking threads

* test/drb/drbtest.rb (test_06_timeout): clean up worker threads
  to avoid leaking threads.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46208 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/drb/drbtest.rb

@@ -191,6 +191,10 @@ module DRbCore
     assert_raise(TimeoutError) do
       @there.do_timeout(ten)
     end
+  ensure
+    DRbService.server.instance_variable_get(:@grp).list.each do |th|
+      th.kill.join
+    end
   end
 
   def test_07_public_private_protected_missing