[FIX] stock: use self instead of picking
[FIX] stock: use self instead of picking

In the compute function _compute_move_without_package, we use self
instead of picking variable, which leads to traceback when more than one
picking is computed

closes odoo/odoo#28482
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo