[FIX] product: error when automatic selecting PO vendor
[FIX] product: error when automatic selecting PO vendor

The business case is the following:
1) The Child company can order the product to the Parent company;
2) The Parent company order the product to a 3rd party supplier.

Settings:
- Enable ‘Inter-Company Transactions’ transactions with the option
  ‘Synchronize sales/purchase orders’ checked;
- Enable 'dropshipping'.

Set 2 companies:
- Parent company;
- Child company: which belongs to the Parent company.

Set a product 'my purchased product':
- Can be Purchased;
- Product Type: Storable Product.
- ‘Purchase’ tab:
  - Set a Vendor price list line 1: which is your Parent company + set
    your Child company who can buy the product;
  - Set a Vendor price list line 2: which is your 3rd party Supplier +
    set your Parent company who can buy the product.
- Log in as the Child company (disable the login in the Parent company,
  select only the Child one);
- Place a Purchase Order for ‘my purchased product’ to vendor 'Parent
  company';
- Confirm the PO.

Before this commit, an error message appears. The issue arises because
seller_ids is retrieved from the cache and not re-read as superuser.
Therefore, records are missing from the list and the correct seller is
not found.

Now, the correct vendor for the purchase order of the parent company is
selected.

opw-2261971

closes odoo/odoo#51887

X-original-commit: 0a9f0c5d2c85e80dd5dceaeacf3f04bfc8aa0be1
Signed-off-by: Jorge Pinna Puissant (jpp) <52c05351c1e024f822a0ec03b4a6cce073666ac8@odoo.com>

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