[FIX] models: backport of 5f660cdb

This fix avoids wild prefetching when serializing
onchange results.

We fell on a strange situation in method `onchange`, where
some data was missing from cache when serializing the
result. In that case, the prefetching overwrites so
many stuff in cache that the results of the onchanges
are lost.
Don't let that happen.

This is a backport of 5f660cdb, with rco-odoo's blessing.
A use case this commit solve is
  - Install the sale app.
  - Create new quotation and assign new partner
  - From inline editable listview add a new order line
  (created the product inline) then directly save.
  - Click on the order line (NOT IN EDIT MODE). This opens
  the order line in a popup.
  - Close the popup.
  - Click edit again.
  - Now change the order line description.
When unfocusing order line field, the description is reset
to previous one.

Closes #23276
Closes #23277