This commit changes TimestampListener to pass a copy of the Carbon
object representing the current time to the entity properties updatedAt
and createdAt. Passing a copy instead of the object itself is needed to
avoid unexpected side effects. Before this change, modifying the time
of the createdAt or updatedAt field of a given entity could affect the
same field of another entity as it could be the same object used inside
TimestampListener for all entities.
[MAILPOET-3870]
2e050d7a32