Raise error if an activestate.yaml script has an empty value.

[mitchell-as]

DX-3219 Error out if script has no value

Sample:

% state run auth 
Operating on project ActiveState/cli, located at /Users/mitchellb/cli.

█ Running Script: auth

 x Invalid script 'auth': 'value' key is empty or missing.

[mitchell-as]

The ARM test failure is expected since ARM projects are not supported on the Platform yet.