Test deferred balance against a range of possible values

Depending of the day of the year, the amount deferred may vary of 2 days.

Closes #12545

modules/account_invoice_defer/tests/scenario_account_invoice_defer.rst

@@ -108,7 +108,7 @@ Check moves on invoice deferred::
     >>> len(deferral.moves)
     13
     >>> accounts['deferred_expense'].reload()
-    >>> accounts['deferred_expense'].balance in {Decimal('270'), Decimal('271')}
+    >>> Decimal('268') <= accounts['deferred_expense'].balance <= Decimal('271')
     True
 
 Define next fiscal year::