Fix - Verification of adding follow-ups for users who are in a ticket…

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes !34517
• Here is a brief description of what this PR does

If a user is part of a group defined as an observer in a ticket, they cannot add a follow-up to this ticket.

If the user is added directly as an individual observer, adding follow-up works correctly.

The problem occurs even if the following options are checked in the user's profile:

• Add follow-up (associated groups)
• Add follow-up (observer)

The same problem occurs with the self-service profile

[cedric-anne]

Could you update the testCanAddFollowupsAsObserver() method to test this case too ?