cli: drop legacy `SafeConfigParser`

The old `SafeConfigParser` class has been deprecated since Python 3.2, and was
fully dropped in Python 3.11. See issue
[#45173](https://bugs.python.org/issue45173) on Python's bugtracker.

/cc @xavier_thompson who may ping anyone else if needed
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

05:05:10

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:37:02

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

02:31:13

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

02:51:17

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:41:27

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

01:33:59

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:39:36

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

04:03:23

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:49:02

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:03:04

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:04:02

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

00:28:16

failed SlapOS.Eggs.UnitTest-Titouan.TestRunner.Lizard

01:24:20