[ruby/yarp] Fix up CI for Ruby 2.5

https://github.com/ruby/yarp/commit/462cb561a9

yarp/templates/template.rb

@@ -314,7 +314,7 @@ module YARP
         ERB.new(template, trim_mode: "-")
       end
     else
-      def erb
+      def erb(template)
         ERB.new(template, nil, "-")
       end
     end