Fix race condition where a namespace would be deleted before a project was deleted

When deleting a user, the following sequence could happen:

1. Project `mygroup/myproject` is scheduled for deletion
2. The group `mygroup` is deleted
3. Sidekiq worker runs to delete `mygroup/myproject`, but the namespace and routes have
   been destroyed.

Closes #30334

app/services/users/destroy_service.rb

@@ -20,10 +20,10 @@ module Users
         Groups::DestroyService.new(group, current_user).execute
       end
 
-      user.personal_projects.each do |project|
+      user.personal_projects.with_deleted.each do |project|
         # Skip repository removal because we remove directory with namespace
         # that contain all this repositories
-        ::Projects::DestroyService.new(project, current_user, skip_repo: true).async_execute
+        ::Projects::DestroyService.new(project, current_user, skip_repo: true).execute
       end
 
       move_issues_to_ghost_user(user)

changelogs/unreleased/sh-fix-destroy-user-race.yml

+---
+title: Fix race condition where a namespace would be deleted before a project was
+  deleted
+merge_request:
+author:

spec/services/users/destroy_spec.rb

@@ -17,13 +17,28 @@ describe Users::DestroyService, services: true do
         expect { Namespace.with_deleted.find(user.namespace.id) }.to raise_error(ActiveRecord::RecordNotFound)
       end
 
-      it 'will delete the project in the near future' do
-        expect_any_instance_of(Projects::DestroyService).to receive(:async_execute).once
+      it 'will delete the project' do
+        expect_any_instance_of(Projects::DestroyService).to receive(:execute).once
 
         service.execute(user)
       end
     end
 
+    context 'projects in pending_delete' do
+      before do
+        project.pending_delete = true
+        project.save
+      end
+
+      it 'destroys a project in pending_delete' do
+        expect_any_instance_of(Projects::DestroyService).to receive(:execute).once
+
+        service.execute(user)
+
+        expect { Project.find(project.id) }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+    end
+
     context "a deleted user's issues" do
       let(:project) { create(:project) }