Pyupgrade to Python 3.9 (#4718)

* Pyupgrade to Python 3.9

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

backtracking/rat_in_maze.py

@@ -1,7 +1,7 @@
-from typing import List
+from __future__ import annotations
 
 
-def solve_maze(maze: List[List[int]]) -> bool:
+def solve_maze(maze: list[list[int]]) -> bool:
     """
     This method solves the "rat in maze" problem.
     In this problem we have some n by n matrix, a start point and an end point.
@@ -70,7 +70,7 @@ def solve_maze(maze: List[List[int]]) -> bool:
     return solved
 
 
-def run_maze(maze: List[List[int]], i: int, j: int, solutions: List[List[int]]) -> bool:
+def run_maze(maze: list[list[int]], i: int, j: int, solutions: list[list[int]]) -> bool:
     """
     This method is recursive starting from (i, j) and going in one of four directions:
     up, down, left, right.