[FIX] web_[sale_]slides: fix courses kanban view layout

[aab-odoo]

This commit fixes the layout of the Courses (e-learning) kanban view, following the conversion to the new kanban API [1]

[1] https://github.com/odoo/odoo/pull/180256

Task~4215979

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:

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[robodoo]