Try to assign automatically planned shipments in the past

Closes #13030
(grafted from e3bd5809ef0341afef8f9b65635d14bd2f9b37d5)

--HG--
branch : 6.0

modules/stock/shipment.py

@@ -79,7 +79,7 @@ class ShipmentAssignMixin(ShipmentMixin):
         return [
             ('company', '=', context.get('company')),
             ('state', '=', 'waiting'),
-            ('planned_date', '=', Date.today()),
+            ('planned_date', '<=', Date.today()),
             ]
 
     @classmethod