[migration] fix handling of default value for boolean attributes We can't assert that the old value is 'True' or 'False', because False used to be stored as an empty string in pre-3.18 versions.

[entity/url publishing] fetch_rqlst should use 'is_instance_of' instead of 'is' We usually want to get any subclasses as well (think Training subclass of Workcase). Closes #3210365.