This update ensures that users always see incomplete tax returns first when viewing a list of returns without any filters. This change prioritizes the display of outstanding returns, making it easier for users to manage their tax obligations. The change was made to improve the user experience and ensure accurate reporting.

When no filters are applied on the tax returns kanban view, incomplete returns should always be displayed before complete ones.

This commit ensure that by ordering tax returns by `is_completed` field.

task-6059414

Forward-Port-Of: odoo/enterprise#114043