MRP with multiple uoms fails to confirm

[juliaprieto]

Module

stock_reserve

Describe the bug

When confirming a manufacturing order with products which have different units of mesurements, an error is raised.
ValueError: Expected singleton: uom.uom(1, 8)
from
stock_reserve/models/stock_reserve.py", line 193, in write
rounding = self.product_uom.rounding

To Reproduce

Affected versions: 14.0 (maybe others)
confirm manufacturing orders

Steps to reproduce the behavior:

1. Create a manufacturing order,
2. Add products with different units of measurements (units, meters, g...)
3. Add amounts available in source stock for each product
4. Confirm manufacturing orders

Expected behavior
Manufacturing order is confirmed and reservations are created for required products

Additional context