missing notebooks to python scripts validation in Github Actions workflow

[shachafl]

This discrepancy was due to the fact that we don't run make validate-notebooks in our Github Actions workflow.
We should add it to starfish-prod-ci.yml

Originally posted by @shachafl in #2195
make validate-notebooks checks if jupyter notebooks and corresponding python scripts are similar.
We should address two issues:

1. Add make validate-notebooks to starfish-prod-ci.yml under starfish-slow.
2. For testing locally, move ipynb_validate_targets from fast to slow testing suite.