[FIX] char_template: avoid duplication of reconciliation model

In some cases it is possible that a plan is the parent of other plans, for example in Spain. Without this condition, the generate_account_reconcile_model method will be called multiple times and create multiple identical reconciliation models, which is not the expected behavior.

This error has already been fixed in 16.0 in another PR (see: https://github.com/odoo/odoo/pull/99581

), but not in 14.0 and 15.0.

closes odoo/odoo#103260

Task-id: 2982600
Signed-off-by: Olivier Colson (oco) <oco@odoo.com>