unset _pulsar on complete
to make sure we can copy.deepcopy the report
@daniel-eggert this resolves our discussion in dasf-messaging-python!37 (comment 40839)
The problem is, that pydantic makes a deepcopy of the objects and for the progress report, this means that the PulsarMessageConsumer
is deepcopied as well which seems to be not a good idea. That is why the _pulsar
is now set to None
when the report is marked as complete.