Closes #32675

Exactly the same changes as in #33640 by @sviande

The PR has been in WIP state for 3 weeks with no activity, and the issue
basically makes Mistral models unusable. I have tested the changes
locally, and it does indeed work. Full credit goes to @sviande, I just
want this feature to be finished.

Release Notes:

- agent: Fixed an issue with tool calling with the Mistral provider
(thanks [@sviande](https://github.com/sviande) and
[@armyhaylenko](https://github.com/armyhaylenko))

Co-authored-by: sviande <sviande@gmail.com>