Update specs to respect Project#namespace_id not null constraint

spec/migrations/cleanup_namespaceless_pending_delete_projects_spec.rb

 require 'spec_helper'
 require Rails.root.join('db', 'post_migrate', '20170502101023_cleanup_namespaceless_pending_delete_projects.rb')
 
-describe CleanupNamespacelessPendingDeleteProjects do
+describe CleanupNamespacelessPendingDeleteProjects, :migration, schema: 20180222043024 do
   before do
     # Stub after_save callbacks that will fail when Project has no namespace
     allow_any_instance_of(Project).to receive(:ensure_storage_path_exists).and_return(nil)

spec/migrations/migrate_issues_to_ghost_user_spec.rb

@@ -8,7 +8,7 @@ describe MigrateIssuesToGhostUser, :migration do
     let(:users) { table(:users) }
 
     before do
-      project = projects.create!(name: 'gitlab')
+      project = projects.create!(name: 'gitlab', namespace_id: 1)
       user = users.create(email: 'test@example.com')
       issues.create(title: 'Issue 1', author_id: nil, project_id: project.id)
       issues.create(title: 'Issue 2', author_id: user.id, project_id: project.id)

spec/models/project_spec.rb

@@ -2499,7 +2499,8 @@ describe Project do
     end
 
     it 'is a no-op when there is no namespace' do
-      project.update_column(:namespace_id, nil)
+      project.namespace.delete
+      project.reload
 
       expect_any_instance_of(Projects::UpdatePagesConfigurationService).not_to receive(:execute)
       expect_any_instance_of(Gitlab::PagesTransfer).not_to receive(:rename_project)
@@ -2531,7 +2532,8 @@ describe Project do
     it 'is a no-op on legacy projects when there is no namespace' do
       export_path = legacy_project.export_path
 
-      legacy_project.update_column(:namespace_id, nil)
+      legacy_project.namespace.delete
+      legacy_project.reload
 
       expect(FileUtils).not_to receive(:rm_rf).with(export_path)
 
@@ -2543,7 +2545,8 @@ describe Project do
     it 'runs on hashed storage projects when there is no namespace' do
       export_path = project.export_path
 
-      project.update_column(:namespace_id, nil)
+      project.namespace.delete
+      legacy_project.reload
 
       allow(FileUtils).to receive(:rm_rf).and_call_original
       expect(FileUtils).to receive(:rm_rf).with(export_path).and_call_original

spec/workers/namespaceless_project_destroy_worker_spec.rb

@@ -22,7 +22,9 @@ describe NamespacelessProjectDestroyWorker do
       end
     end
 
-    context 'project has no namespace' do
+    # Only possible with schema 20180222043024 and lower.
+    # Project#namespace_id has not null constraint since then
+    context 'project has no namespace', :migration, schema: 20180222043024 do
       let!(:project) do
         project = build(:project, namespace_id: nil)
         project.save(validate: false)