[FIX] mail: tracking_value_ids field group

Give a coherent group as otherwise we could have access errors. Simple
case: an Admin Rights user goes into a mail message form which is only
available in debug mode which sets `group.no_one` into such user. This
model is only readeable by `base.group_sytem` so an AccessError will
raise.

closes odoo/odoo#67621

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>