(PC-31411)[API] fix: collective pending booking: rm confirmation date

A collective pending booking should not have a confirmation since it
should not have been confirmed.

api/src/pcapi/core/educational/factories.py

@@ -275,6 +275,7 @@ class CancelledCollectiveBookingFactory(CollectiveBookingFactory):
 class PendingCollectiveBookingFactory(CollectiveBookingFactory):
     cancellationLimitDate = factory.LazyFunction(lambda: datetime.datetime.utcnow() + datetime.timedelta(days=10))
     confirmationLimitDate = factory.LazyFunction(lambda: datetime.datetime.utcnow() + datetime.timedelta(days=10))
+    confirmationDate = None
     status = models.CollectiveBookingStatus.PENDING