[FIX] purchase_stock: compute_picking perfs improvements

Backport odoo/odoo#35878, adding an explicit mapped
because Relational.__get__ introduced in 13.0.

closes odoo/odoo#72469

Signed-off-by: Rémy Voet <ryv-odoo@users.noreply.github.com>

addons/purchase_stock/models/purchase.py

@@ -33,17 +33,10 @@ class PurchaseOrder(models.Model):
     group_id = fields.Many2one('procurement.group', string="Procurement Group", copy=False)
     is_shipped = fields.Boolean(compute="_compute_is_shipped")
 
-    @api.depends('order_line.move_ids.returned_move_ids',
-                 'order_line.move_ids.state',
-                 'order_line.move_ids.picking_id')
+    @api.depends('order_line.move_ids.picking_id')
     def _compute_picking(self):
         for order in self:
-            pickings = self.env['stock.picking']
-            for line in order.order_line:
-                # We keep a limited scope on purpose. Ideally, we should also use move_orig_ids and
-                # do some recursive search, but that could be prohibitive if not done correctly.
-                moves = line.move_ids | line.move_ids.mapped('returned_move_ids')
-                pickings |= moves.mapped('picking_id')
+            pickings = order.order_line.mapped('move_ids.picking_id')
             order.picking_ids = pickings
             order.picking_count = len(pickings)