Make link tracker handle other types than many2one for tracking fields. Currently, when a field of type char is returned, an error occurs. odoo/addons/utm/models/utm_mixin.py already handles other types than many2one for tracking_fields(). This aligns to that behaviour in the link tracker. opw-2494686 closes odoo/odoo#71780 X-original-commit: a2068f9696917d7fa4848bc09d05eced84d0cc2f Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>