[FIX] stock: do not write on picking type

When creating a stock.picking, the related fields picking_type_entire_packs and
picking_type_code were both updated.
This was an issue was required write access on stock.picking.type (warehouse
manager) to create a stock.picking (warehouse user).

The fields were updated as they were present in the view and filled with the
related value. Even if the value was unchanged, it was triggering a write
anyway.

The two fields were in invisible="1" and used only in attrs for other fields.

Making these two fields in readonly does not prevent to use it in the attrs but
avoid to send a value to the server and trigger a useless write.

Fixes #15769

addons/stock/models/stock_picking.py

@@ -245,8 +245,10 @@ class Picking(models.Model):
     picking_type_code = fields.Selection([
         ('incoming', 'Vendors'),
         ('outgoing', 'Customers'),
-        ('internal', 'Internal')], related='picking_type_id.code')
-    picking_type_entire_packs = fields.Boolean(related='picking_type_id.show_entire_packs')
+        ('internal', 'Internal')], related='picking_type_id.code',
+        readonly=True)
+    picking_type_entire_packs = fields.Boolean(related='picking_type_id.show_entire_packs',
+        readonly=True)
 
     quant_reserved_exist = fields.Boolean(
         'Has quants already reserved', compute='_compute_quant_reserved_exist',