During a credit time period where the employee works zero hours,
the employee should still be able to take maternity leave.
Before this change this was only possible if you manually set the
duration of this leave for it to be non-zero, which was kind of a hack.
Now that durations are computed correctly automatically, maternity (and
paternity) leaves were added to the list of exceptions of leave types
that can be taken even if their duration is zero.
Part-of: odoo/odoo#119317
Rob Coekaerts
8f4e365ad7