purchase_stock, point_of_sale, sale_mrp

What are the steps to reproduce your issue?
When Odoo.sh runs unit tests on a development branch,
it tests the code in the MRP module for rounding errors.

What is the current behavior that you observe?
I had a customization that introduced a rounding error in the standard MRP module.
When the unit tests ran on the development branch, I got a traceback.

What would be your expected behavior in this case?
The rounding error should be reported as a failed test with a message. No traceback.

opw-3454998

closes odoo/odoo#131418

Signed-off-by: William Henrotin (whe) <whe@odoo.com>