Fix factorybot failures after bump to v5

The default value for `FactoryBot.use_parent_strategy` changed from `false`
to `true` at [v5.0.0](thoughtbot/factory_bot_rails#314)

This caused some validation errors in role creation in tests because the
attached role assignments weren't created correctly due to the new FactoryBot
configuration.

We could set `FactoryBot.use_parent_strategy = false`, but I think it's
better to update the factories themselves.

test/factories/roles.rb

@@ -16,13 +16,13 @@
 
   trait :occupied do
     after :build do |role, _|
-      role.role_appointments = [FactoryBot.build(:role_appointment)]
+      role.role_appointments = [FactoryBot.create(:role_appointment)]
     end
   end
 
   trait :vacant do
     after :build do |role, _|
-      role.role_appointments = [FactoryBot.build(:role_appointment, :ended)]
+      role.role_appointments = [FactoryBot.create(:role_appointment, :ended)]
     end
   end
 end