Modify Namespace spec factory to always have a type

Because `nil` type implicitly meant 'User' namespace, and we are phasing out `nil` namespace type.

spec/factories/namespaces.rb

 # frozen_string_literal: true
 
 FactoryBot.define do
-  factory :namespace do
+  # This factory is called :namespace but actually maps (and always has) to User type
+  # See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74152#note_730034103 for context
+  factory :namespace, class: 'Namespaces::UserNamespace' do
     sequence(:name) { |n| "namespace#{n}" }
+    type { Namespaces::UserNamespace.sti_name }
+
     path { name.downcase.gsub(/\s/, '_') }
 
     owner { association(:user, strategy: :build, namespace: instance, username: path) }

spec/models/namespace/traversal_hierarchy_spec.rb

@@ -21,7 +21,7 @@ RSpec.describe Namespace::TraversalHierarchy, type: :model do
     end
 
     context 'with group outside of hierarchy' do
-      let(:group) { create(:namespace) }
+      let(:group) { create(:group) }
 
       it { expect(hierarchy.root).not_to eq root }
     end

spec/support/shared_examples/requests/api/pypi_packages_shared_examples.rb

@@ -346,7 +346,8 @@ RSpec.shared_examples 'a pypi user namespace endpoint' do
   end
 
   with_them do
-    let_it_be_with_reload(:group) { create(:namespace) }
+    # only groups are supported, so this "group" is actually the wrong namespace type
+    let_it_be_with_reload(:group) { create(:user_namespace) }
     let(:headers) { user_role == :anonymous ? {} : basic_auth_header(user.username, personal_access_token.token) }
 
     before do