Fixed tempfile leak.

From: SHIBATA Hiroshi <hsbt@ruby-lang.org>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62424 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rubygems/test_gem_package_tar_header.rb

@@ -160,6 +160,7 @@ group\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000
       assert_raises ArgumentError do
         new_header = Gem::Package::TarHeader.from io
       end
+      io.close! if io.respond_to? :close!
     end
   end