[16.0] - sale_triple_discount - updating discounts not working after sale.order.line creation

[IJOL]

Module

sale_triple_discount

Describe the bug

After line creation updating discounts is not working the previous value is reapplied

Steps to reproduce the behavior:

1. Create a valid sale.order.line applying some discounts
2. Try to update any of them
3. try to save the updates, line will recover previous unmodified state

Expected behavior
Been able to update discounts after line creation

[IJOL]

#3324 seems to solve it, but it maybe not totally ok

[IJOL]

a better solution in #3329

[github-actions]

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