tabs instead of spaces in exercise 4.5

[lethargosapatheia]

Here:
https://github.com/dabeaz-course/practical-python/blob/master/Notes/04_Classes_objects/02_Inheritance.md#exercise-45-an-extensibility-problem

There are tabs before the "raise" directives instead of spaces. I've come across this randomly when I saw that forgejo was displaying it differently (made it look like they were part of the class definitions) than on github. So you cannot copy/paste that code and use it as such. Which I generally don't do anyway, but in this case it was really misleading, because I thought the 'raise' directives were intentionally part of the class methods/definitions for some reason.