[FIX] sale: not change the package type when setting the package qty

Current behaviour:
Changing the package quantity may change the package type,
leading to an incoherent product quantities in the SOL.
(For ex: 20 uom in 2 packages of 20)

Expected behaviour:
When setting the package quantity, don't change the
package type. If the user wants to change the package type
they can do it by manually setting it or changing the product_uom.

Steps to reproduce:
- Install Sale and Inventory
- Activate Packages in settings
- Create 2 package types for a product of choice, one of 10, another of 20
- Create a new SO with that product
- Set the quantity to 10 (a new package_qty=1 and packaging type of 10 should appear)
- Save
- Edit package_qty to 2
- Observe that we have 20 units of the product, 2 packages of 20,
  instead of 2 packages of 10

Reason for the problem:
When setting the `product_packaging_qty`, the `product_uom_qty` compute is triggered.
When `product_uom_qty` changes, it triggers `product_packaging_id`'s compute.
When `product_packaging_id` is computed, it doesn't trigger `product_package_qty`,
because it is protected, since we are writing to it.

Fix:
When we are writing the `product_packaging_qty` and the `product_uom_qty`
we remove the compute for `product_packaging_id`.

Affected versions:
- saas-15.2
- saas-15.3
- 16.0
- master

opw-3010703

closes odoo/odoo#106811

X-original-commit: 42c9f7fb2287e4653999d5a5ce010547e9c3712f
Signed-off-by: Piryns Victor (pivi) <pivi@odoo.com>