test/readline/test_readline.rb: Close fds.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46234 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/readline/test_readline.rb

@@ -469,6 +469,7 @@ class TestReadline < Test::Unit::TestCase
           STDOUT.reopen(orig_stdout)
           orig_stdin.close
           orig_stdout.close
+          orig_stderr.close
         end
       }
     }