The `difference()` filter inputs a list, and takes another list as
parameter, computes a set difference between the two, and returns
the resulting (unordered) list.
This is documented here:
https://docs.ansible.com/ansible/latest/collections/ansible/builtin/difference_filter.html
This filter was changed in:
7d3d4572ed
The behaviour changed in ansible-core between 2.15 and 2.16:
```
 ################################################################
 ### Testing ansible-core==2.16
 ################################################################
 PLAY [Test ansible difference filter] ******************************************
 TASK [debug] *******************************************************************
 ok: [localhost] => {
 "msg": "diff with a string: ['one', 'two', 'six'] | difference('two') => ['one', 'six', 'two']"
 }
 TASK [debug] *******************************************************************
 ok: [localhost] => {
 "msg": "diff with a list: ['one', 'two', 'six'] | difference(['two']) => ['one', 'six']"
 }
 PLAY RECAP *********************************************************************
 localhost : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
 ################################################################
 ### Testing ansible-core==2.15
 ################################################################
 PLAY [Test ansible difference filter] ******************************************
 TASK [debug] *******************************************************************
 ok: [localhost] => {
 "msg": "diff with a string: ['one', 'two', 'six'] | difference('two') => ['one', 'six']"
 }
 TASK [debug] *******************************************************************
 ok: [localhost] => {
 "msg": "diff with a list: ['one', 'two', 'six'] | difference(['two']) => ['one', 'six']"
 }
 PLAY RECAP *********************************************************************
 localhost : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0
```
The above was generated by using: https://github.com/vincent-legoll/test_ansible_diff
Closes-Bug: #2096936
Change-Id: I7a57c829803fc5baa8b1d3a1805c102f04b8ab2c
Signed-off-by: Vincent Legoll <vincent.legoll@iphc.cnrs.fr>