[FIX] doc: Update Kanban Exercise code
[FIX] doc: Update Kanban Exercise code

Field name was incorrecty spelt. Replace 'openacad.session.kanban'
with 'openacademy.session.kanban'

closes odoo/odoo#37736

X-original-commit: 1043d1622947614d2d4e7f237c73e1b92191d099
Signed-off-by: Martin Trigaux (mat) <cc7c5be316e48d137cbb549833b85d91034d799d@odoo.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo