[FIX] purchase_stock: confirm push pickings

When creating a Purchase Order with multi-step reception, the pickings
created by the push rules won't get confirmed as they should be (like in
the sales multi-step flow).

This creates issues further down with auto-batch as created pickings
don't get auto-batched even if the picking type is set to do it.

Task-2971346

X-original-commit: dc517bbe7ffbae8a8774f705c9431dce45c461ba
Part-of: odoo/odoo#102382

addons/purchase_stock/models/purchase.py

@@ -245,7 +245,9 @@ class PurchaseOrder(models.Model):
                     seq += 5
                     move.sequence = seq
                 moves._action_assign()
-                pickings.action_confirm()
+                # Get following pickings (created by push rules) to confirm them as well.
+                forward_pickings = self.env['stock.picking']._get_impacted_pickings(moves)
+                (pickings | forward_pickings).action_confirm()
                 picking.message_post_with_view('mail.message_origin_link',
                     values={'self': picking, 'origin': order},
                     subtype_id=self.env.ref('mail.mt_note').id)