Stale read on CreateModelVersion

Refs teklia/requests#879

.using('default') is missing from https://gitlab.com/teklia/arkindex/backend/-/blob/bb5c34518c009b94c8696c74a844b2c12fd3e44e/arkindex/training/api.py#L76, so creating a model version immediately after creating a model might not be able to find the model if there's even the slightest amount of replication lag.