restore the behavior of parameter many in the serializers

[dem4ply]

is restoring the parameter many=true when is validated the data
previously was removing the parameter and always return a simple serializer and not the list serializer
when you try to run save result in an exception

[davidzwa]

@dem4ply please have a look at the CI for the failing checks!

[dem4ply]

i read the error and for be honest i dont know how to fix that error
perhaps the next week i can put some time for see how to fix the problem