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>

matrix/searching_in_sorted_matrix.py

@@ -1,10 +1,8 @@
 from __future__ import annotations
 
-from typing import Union
-
 
 def search_in_a_sorted_matrix(
-    mat: list[list], m: int, n: int, key: Union[int, float]
+    mat: list[list], m: int, n: int, key: int | float
 ) -> None:
     """
     >>> search_in_a_sorted_matrix(