[FIX] stock: incorrect domain

The field `parent_id` has been removed in
https://github.com/odoo/odoo/commit/809605bb8f16cf1398ff5070ec0d5bd568aef343#diff-807e5ce512b0669468b040be7a9c470fL236

Therefore, `child_of` cannot be used anymore.

Closes #26850
opw-1883655

closes odoo/odoo#27083

addons/stock/models/stock_quant.py

@@ -480,7 +480,7 @@ class QuantPackage(models.Model):
         return action
 
     def _get_contained_quants(self):
-        return self.env['stock.quant'].search([('package_id', 'child_of', self.ids)])
+        return self.env['stock.quant'].search([('package_id', 'in', self.ids)])
 
     def _get_all_products_quantities(self):
         '''This function computes the different product quantities for the given package