[FIX] pos_self_order: fix kiosk not closing

[vlst-odoo]

When the session of the kiosk is closed in the backoffice, the kiosk is supposed to show the "We are closed" banner and to no longer accept orders. Currently, this is not the case.

In this commit we fix the issue

Task: 4219525

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[robodoo]

[davidmonnom]

@robodoo r+