Address review comments

changelogs/unreleased/refactor_namespace_all_projects.yml

----
-title: Add recursive approach to Namespace#all_projects
-merge_request: 44740
-author:
-type: changed

ee/spec/services/update_build_minutes_service_spec.rb

@@ -46,15 +46,15 @@ RSpec.describe UpdateBuildMinutesService do
         end
       end
 
-      context 'when namespace is subgroup' do
+      context 'when group is subgroup' do
         let(:root_ancestor) { create(:group, shared_runners_minutes_limit: 100) }
-        let(:namespace) { create(:namespace, parent: root_ancestor) }
+        let(:namespace) { create(:group, parent: root_ancestor) }
 
-        it 'creates a statistics in root namespace' do
+        it 'creates a statistics in root group' do
           subject
 
-          expect(root_ancestor.namespace_statistics&.shared_runners_seconds)
-            .to be_nil
+          expect(root_ancestor.namespace_statistics.reload.shared_runners_seconds)
+            .to eq(build.duration.to_i * 2)
         end
 
         context 'with disabled feature flag :recursive_approach_for_all_projects in Namespace#all_projects' do
@@ -62,7 +62,7 @@ RSpec.describe UpdateBuildMinutesService do
             stub_feature_flags(recursive_approach_for_all_projects: false)
           end
 
-          it 'creates a statistics in root namespace' do
+          it 'creates a statistics in root group' do
             subject
 
             expect(root_ancestor.namespace_statistics.reload.shared_runners_seconds)

spec/models/namespace_spec.rb

@@ -856,10 +856,10 @@ RSpec.describe Namespace do
 
   describe '#all_projects' do
     shared_examples 'all projects for a namespace' do
-      let(:group) { create(:group) }
-      let(:child) { create(:group, parent: group) }
-      let!(:project1) { create(:project_empty_repo, namespace: group) }
-      let!(:project2) { create(:project_empty_repo, namespace: child) }
+      let_it_be(:group) { create(:group) }
+      let_it_be(:child) { create(:group, parent: group) }
+      let_it_be(:project1) { create(:project_empty_repo, namespace: group) }
+      let_it_be(:project2) { create(:project_empty_repo, namespace: child) }
 
       it { expect(group.all_projects.to_a).to match_array([project2, project1]) }
       it { expect(child.all_projects.to_a).to match_array([project2]) }