[common][serializers] Update code using annotate_full_name

beat/web/common/serializers.py

@@ -422,7 +422,7 @@ class ContributionCreationSerializer(ContributionModSerializer):
 
         if previous_version is not None:
             try:
-                previous_object = annotate_full_name(self.Meta.model).get(
+                previous_object = annotate_full_name(self.Meta.model.objects).get(
                     full_name=previous_version
                 )
             except self.Meta.model.DoesNotExist:
@@ -449,7 +449,7 @@ class ContributionCreationSerializer(ContributionModSerializer):
                 raise serializers.ValidationError("A fork starts at 1")
 
             try:
-                forked_of_object = annotate_full_name(self.Meta.model).get(
+                forked_of_object = annotate_full_name(self.Meta.model.objects).get(
                     full_name=fork_of
                 )
             except self.Meta.model.DoesNotExist: