Deduce the commission price from the cost

Because the commission price is negative when it has the same type as the
invoice.

issue11723
review423891003

stock_reporting_margin.py

@@ -20,7 +20,7 @@ class AbstractCommissionMixin:
         cost = super()._column_cost(tables, withs, sign)
         if (Transaction().context.get('include_commission')
                 and 'commission_price' in Move._fields):
-            cost += Sum(
+            cost -= Sum(
                 sign * cls.cost.sql_cast(move.internal_quantity)
                 * Coalesce(move.commission_price, 0))
         return cost

tests/scenario_commission_stock.rst

@@ -191,7 +191,7 @@ Check reporting margin::
     >>> context['include_commission'] = True
     >>> with config.set_context(context=context):
     ...     report, = MarginProduct.find([])
-    >>> report.cost == Decimal('225.0000')
+    >>> report.cost == Decimal('275.0000')
     True
     >>> report.revenue == Decimal('500.0000')
     True