authentication_policy: fix display of password expiration date

7a9d47adff (authentication_policy: fix display of password expiration date, 2021-03-25)
was wrong, the date was not properly substituted in the message.
8 jobs for feat/deferred_style_alarm in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

passed ERP5.PerformanceTest-Master

failed ERP5.UnitTest-Master

failed ERP5.UnitTest-Master.Medusa

passed SlapOS.Eggs.UnitTest-Master.Python2

00:18:52

passed SlapOS.Eggs.UnitTest-Master.Python3

00:15:53

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

00:09:52