test_regexp.rb: suppress warning
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54537 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_regexp.rb: suppress warning
"assigned but unused variable" warning by prefixing '_'.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54537 b2dd03c8-39d4-4d8f-98ff-823fe69b080e