Use default_enabled: :yaml for feature flag check

The runner_registration_control FF YAML file is defaulting to false, so
there is no change in logic

app/policies/group_policy.rb

@@ -81,7 +81,7 @@ class GroupPolicy < Namespaces::GroupProjectNamespaceSharedPolicy
   condition(:crm_enabled, score: 0, scope: :subject) { Feature.enabled?(:customer_relations, @subject) && @subject.crm_enabled? }
 
   condition(:group_runner_registration_allowed) do
-    Feature.disabled?(:runner_registration_control) || Gitlab::CurrentSettings.valid_runner_registrars.include?('group')
+    Feature.disabled?(:runner_registration_control, default_enabled: :yaml) || Gitlab::CurrentSettings.valid_runner_registrars.include?('group')
   end
 
   rule { can?(:read_group) & design_management_enabled }.policy do

app/policies/project_policy.rb

@@ -195,7 +195,7 @@ class ProjectPolicy < BasePolicy
   end
 
   condition(:project_runner_registration_allowed) do
-    Feature.disabled?(:runner_registration_control) || Gitlab::CurrentSettings.valid_runner_registrars.include?('project')
+    Feature.disabled?(:runner_registration_control, default_enabled: :yaml) || Gitlab::CurrentSettings.valid_runner_registrars.include?('project')
   end
 
   # `:read_project` may be prevented in EE, but `:read_project_for_iids` should

app/services/ci/runners/register_runner_service.rb

@@ -47,7 +47,7 @@ module Ci
       end
 
       def runner_registrar_valid?(type)
-        Feature.disabled?(:runner_registration_control) || Gitlab::CurrentSettings.valid_runner_registrars.include?(type)
+        Feature.disabled?(:runner_registration_control, default_enabled: :yaml) || Gitlab::CurrentSettings.valid_runner_registrars.include?(type)
       end
 
       def token_scope

app/views/admin/application_settings/ci_cd.html.haml

@@ -39,7 +39,7 @@
     .settings-content
       = render 'registry'
 
-- if Feature.enabled?(:runner_registration_control)
+- if Feature.enabled?(:runner_registration_control, default_enabled: :yaml)
   %section.settings.as-runner.no-animate#js-runner-settings{ class: ('expanded' if expanded_by_default?) }
     .settings-header
       %h4