test_variable.rb: suppress warnings

* test/ruby/test_variable.rb (ruler4): suppress warning.
  (test_global_variable_poped, test_constant_poped): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48540 b2dd03c8-39d4-4d8f-98ff-823fe69b080e