test_module.rb: test with UTF-8

* test/ruby/test_module.rb (test_uninitialized_instance_variable):
  test with UTF-8 default external encoding for non-locale
  environments.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48051 b2dd03c8-39d4-4d8f-98ff-823fe69b080e