Code inspection by SERVER-108332 found that in change_stream_event_transform.cpp we are using the buckets namespace to determine the collection type. https://github.com/mongodb/mongo/blob/143c9495c7f3a2134c9b1f72320ef94235b8f1b2/src/mongo/db/pipeline/change_stream_event_transform.cpp#L134-L137

We should review this logic for viewless timeseries collections, which don't have a separate system.buckets namespace.