Speed up project model specs by using factory default for namespace

spec/models/project_spec.rb

@@ -2,12 +2,14 @@
 
 require 'spec_helper'
 
-RSpec.describe Project do
+RSpec.describe Project, factory_default: :keep do
   include ProjectForksHelper
   include GitHelpers
   include ExternalAuthorizationServiceHelpers
   using RSpec::Parameterized::TableSyntax
 
+  let_it_be(:namespace) { create_default(:namespace) }
+
   it_behaves_like 'having unique enum values'
 
   describe 'associations' do