Make __ac_local_roles__ stable

Otherwise, the object could be modified (_p_changed=1) and reindexed for nothing.
3 jobs for listbox_use_domsugar in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-Master

01:41:38

passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:36

passed SlapOS.Eggs.UnitTest-Master.Python3

00:10:08