limit to change detection stimulus blocks in VBO Expt Data .md

if you dont limit to `change_detection_behavior` block, you get NaNs in `image_name` column of `stimulus_presentations`, which causes this error: 

<img width="807" alt="image" src="https://github.com/user-attachments/assets/319f4c8d-2360-4503-a598-a5c6582b93cc">
