test_system.rb: commit miss

* test/ruby/test_system.rb (TestSystem#test_system_redirect_win): fix
  intentional failure left carelessly.  [Bug #7482]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38958 b2dd03c8-39d4-4d8f-98ff-823fe69b080e