Fix: cover add-tile button rights with a regression test

[Rom1-B]

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 !45219
• Ensures the "Add tile" button on the helpdesk home configuration page only appears for users who actually have the rights to add a tile.

Screenshots (if appropriate):

[AdrienClairembault]

Did you forget to push part of the code?

It seems to me the current code is incomplete, you didn't modify any behavior.
I would say you added the canAddTile method to use its result as a condition in a twig template somewhere but it don't see it in the diff.

This also mean that the added tests proves nothing as there are no behavioral changes here.