[FIX] stock: show exception log when cancel backorders

Steps to Reproduce Issue for single picking:
1. Install Sales, Inventory
2. Create an SO and confirm
3. Go to the transfer, assign the done value to be less than demanded
4. Validate the transfer and cancel the backorder

Current Behavior:
There is no exception error on the SO chatter

Expected Behavior:
An exception error should be logged on the SO chatter

Other Info: When cancelling a backorder for a single picking,
the exception error about less quantity than expected is not logged on the SO.
"process_cancel_backorder" does not call _log_less_quantities_than_expected.
As defined in "process", the exception is only logged when validating multiple pickings at once but
one is to backorder but the other is not.

opw-3222508

closes odoo/odoo#120994

X-original-commit: 92cd7d08
Signed-off-by: Tiffany Chang <tic@odoo.com>