Do not fail on leap day to create next fiscal year

Replace the year of a date is not safe, it is better to use relativedelta.

Closes #13064
(grafted from 4b19fb0bc801a784139c0c6245d8649480e13280)

--HG--
branch : 6.0

modules/account/tests/test_account.py

@@ -381,7 +381,7 @@ class AccountTestCase(
             # Use next fiscalyear
             today = datetime.date.today()
             next_fiscalyear = get_fiscalyear(company,
-                today=today.replace(year=today.year + 1))
+                today=today + relativedelta(years=1))
             next_fiscalyear.save()
             FiscalYear.create_period([next_fiscalyear])