[rails6][rbac/filterer_spec.rb] Use .default_scoped

Adds a fix for the following deprecation error:

  DEPRECATION WARNING: Class level methods will no longer inherit
  scoping from `create!` in Rails 6.1. To continue using the scoped
  relation, pass it into the block directly. To instead access the full
  set of models, as Rails 6.1 will, use `Vm.default_scoped`.

  (called from validate_each at /Users/nicklamuro/code/redhat/manageiq/spec/lib/rbac/filterer_spec.rb:2086)

This was added to fix "leaking scopes" in Rails 6.1, but was added as a
deprecation warning first:

- rails/rails#35280
- rails/rails#37727

This specifically was just a fake `Vm` model specifically used for the Rbac
specs, so this isn't something that needs to be fixed in the app codebase
proper.

spec/lib/rbac/filterer_spec.rb

@@ -2082,8 +2082,8 @@ def get_rbac_results_for_and_expect_objects(klass, expected_objects)
           vm.tag_with(@tags.values.join(" "), :ns => "*") if i > 0
         end
 
-        Vm.scope :group_scope,    ->(group_num) { Vm.where("name LIKE ?", "Test Group #{group_num}%") }
-        Vm.scope :is_on,          ->            { Vm.where(:power_state => "on") }
+        Vm.scope :group_scope,    ->(group_num) { Vm.default_scoped.where("name LIKE ?", "Test Group #{group_num}%") }
+        Vm.scope :is_on,          ->            { Vm.default_scoped.where(:power_state => "on") }
       end
 
       context ".search" do