suppress warning: attempt to close unfinished zstream; reset forced.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57127 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/zlib/test_zlib.rb

@@ -213,7 +213,9 @@ if defined? Zlib
       z = Zlib::Deflate.new
       z << "foo"
       assert_raise(Zlib::StreamError) { z.set_dictionary("foo") }
-      z.close # without this, outputs `zlib(finalizer): the stream was freed prematurely.'
+      EnvUtil.suppress_warning do
+        z.close # without this, outputs `zlib(finalizer): the stream was freed prematurely.'
+      end
     end
 
     def test_reset