Detect if we should expose environment_scope by

checking against if it's responding to environment_scope
directly. See:

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12936#note_36822301

lib/api/entities.rb

@@ -863,11 +863,9 @@ module API
 
       # EE
       expose :environment_scope, if: ->(variable, options) {
-        if variable.respond_to?(:project)
-          variable.project
-        else
-          variable.group
-        end.feature_available?(:variable_environment_scope)
+        if variable.respond_to?(:environment_scope)
+          variable.project.feature_available?(:variable_environment_scope)
+        end
       }
     end