Mixpanel information json serialization (#2190)

# Description

User reported error message due to failed mixpanel serialization. The
error was eliminated by setting mode=json on Pydantic method.

<img width="1540" height="1030" alt="Screenshot 2025-11-12 at 10 40 22"
src="https://github.com/user-attachments/assets/08b9ca03-156d-4350-9239-6b2267240a37"
/>




## Changelog

- [x] Patch
- [ ] Skip

## cdf

### Fixed

- Error on tracking info serielization

## templates

No changes.
