void return type in L_fun unable to be type checked

[mpahrens]

When making an example program following the L_fun grammar, I expect the following program to be able to parse and type check:

def foo() -> void :
   print(1)

the type annotation, void, gets parsed as Name('void') similar to int and bool.

In type_check_Lfun.py, there is no case for Name('void') and so type checking the program causes an error instead:

def parse_type_annot(self, annot):
      match annot:
        case Name(id):
          if id == 'int':
            return IntType()
          elif id == 'bool':
            return BoolType()
          else:
            raise Exception('parse_type_annot: unexpected ' + repr(annot))

Exception: parse_type_annot: unexpected Name('void')

Omitting the -> void return type annotation causes the python.ast parser to put a None as the return type annotation rather than VoidType() like we might expect.

Adding a case for id == 'void' seems to work, but before I make a pull request, I wanted to see if I am missing anything by doing so.
Since VoidType() has an explicit case in parse_type_annot(...), I could imagine that there is another way for the parser to produce a VoidType() annotation itself without me adding this case.

Thanks!