[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: 1043d162
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

doc/howtos/backend/exercise-kanban

@@ -22,7 +22,7 @@ Index: addons/openacademy/views/openacademy.xml
          </record>
  
 +        <record model="ir.ui.view" id="view_openacad_session_kanban">
-+            <field name="name">openacad.session.kanban</field>
++            <field name="name">openacademy.session.kanban</field>
 +            <field name="model">openacademy.session</field>
 +            <field name="arch" type="xml">
 +                <kanban default_group_by="course_id">