Fix managed_free_namespaces scope

Don’t rely on Namespace#plan_id column, but
instead joing with gitlab_subscriptions

changelogs/unreleased/208894-fix-showing-only-free-namespaces-when-applying-licenses.yml

+---
+title: Fix managed_free_namespaces scope to only groups without a license or a free license
+merge_request: 27356
+author:
+type: fixed

ee/app/helpers/subscriptions_helper.rb

@@ -37,7 +37,7 @@ module SubscriptionsHelper
   end
 
   def group_data
-    current_user.managed_free_namespaces.map do |namespace|
+    current_user.managed_free_namespaces.with_counts(archived: false).map do |namespace|
       {
         id: namespace.id,
         name: namespace.name,

ee/app/models/ee/user.rb

@@ -243,7 +243,10 @@ module EE
     end
 
     def managed_free_namespaces
-      manageable_groups.with_counts(archived: false).where(plan: [nil, Plan.free, Plan.default]).order(:name)
+      manageable_groups
+        .left_joins(:gitlab_subscription)
+        .merge(GitlabSubscription.left_joins(:hosted_plan).where(plans: { name: [nil, *Plan::DEFAULT_PLANS] }))
+        .order(:name)
     end
 
     override :has_current_license?

ee/spec/models/user_spec.rb

@@ -941,9 +941,9 @@ describe User do
 
   describe '#managed_free_namespaces' do
     let_it_be(:user) { create(:user) }
-    let_it_be(:licensed_group) { create(:group, plan: :bronze_plan) }
-    let_it_be(:free_group_z) { create(:group, plan: :default_plan, name: 'Z') }
-    let_it_be(:free_group_a) { create(:group, plan: :default_plan, name: 'A') }
+    let_it_be(:licensed_group) { create(:group, gitlab_subscription: create(:gitlab_subscription, :bronze)) }
+    let_it_be(:free_group_z) { create(:group, name: 'Z', gitlab_subscription: create(:gitlab_subscription, :free)) }
+    let_it_be(:free_group_a) { create(:group, name: 'A', gitlab_subscription: create(:gitlab_subscription, :free)) }
 
     subject { user.managed_free_namespaces }