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>

sorts/quick_sort.py

@@ -7,7 +7,7 @@ python3 -m doctest -v quick_sort.py
 For manual testing run:
 python3 quick_sort.py
 """
-from typing import List
+from __future__ import annotations
 
 
 def quick_sort(collection: list) -> list:
@@ -27,8 +27,8 @@ def quick_sort(collection: list) -> list:
     if len(collection) < 2:
         return collection
     pivot = collection.pop()  # Use the last element as the first pivot
-    greater: List[int] = []  # All elements greater than pivot
-    lesser: List[int] = []  # All elements less than or equal to pivot
+    greater: list[int] = []  # All elements greater than pivot
+    lesser: list[int] = []  # All elements less than or equal to pivot
     for element in collection:
         (greater if element > pivot else lesser).append(element)
     return quick_sort(lesser) + [pivot] + quick_sort(greater)