Fix var type annotation

Author: sheida-shab

sprint5-prep/prep9-exercise.py

@@ -10,7 +10,7 @@ def get_name(self) -> str:
 class Child(Parent):
     def __init__(self, first_name: str, last_name: str):
         super().__init__(first_name, last_name)
-        self.previous_last_names = []
+        self.previous_last_names: list[str] = []
 
     def change_last_name(self, last_name) -> None:
         self.previous_last_names.append(self.last_name)