Fixed two more type hints in the parser visitor

Author: knutwannheden

rewrite/rewrite/python/_parser_visitor.py

@@ -2149,11 +2149,11 @@ def __skip(self, tok: Optional[str]) -> Optional[str]:
             self._cursor += len(tok)
         return tok
 
-    def __whitespace(self, stop: str = None) -> Space:
+    def __whitespace(self, stop: Optional[str] = None) -> Space:
         space, self._cursor = self.__format(self._source, self._cursor, stop)
         return space
 
-    def __format(self, source: str, offset: int, stop: str = None) -> Tuple[Space, int]:
+    def __format(self, source: str, offset: int, stop: Optional[str] = None) -> Tuple[Space, int]:
         prefix = None
         whitespace = []
         comments = []