wrong revision id for concurrent edits

when two people create revisions at the same time because they are editing the content, we can get wrong notifications. One example is https://hcdc.hzg.de/clm-community/clm-manager/notifications/systemnotification/6/change/?_changelist_filters=q%3Dalex

this line is the cause for it: https://coastgit.hzg.de/hcdc/django/clm-community/django-academic-community/-/blob/master/academic_community/history/views.py#L62