LFortran kernel does not run program body in notebooks

See https://stackoverflow.com/questions/70825597/lfortran-in-a-jupyter-notebook-kills-kernel

This could be a bug in LFortran not executing programs defined in the global scope when running as notebook kernel. Not sure what the best way is to track this down and generate a reproducer.

Also, congratulation to your first question on stackoverflow in the lfortran category.