Revert "The setter for a RelatedManager type attribute (reverse relation) of a Django model requires the value to be set to be a list even if it would consist of only one object like in this save_related method that is fixed in this commit. Otherwise, Django raises TypeError in django/db/models/fields/related.py __set__ of ForeignRelatedObjectsDescriptor:"

This reverts commit 000fbbf17110d37ef68596a28d538447790731d8.