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>

arithmetic_analysis/newton_forward_interpolation.py

@@ -1,7 +1,7 @@
 # https://www.geeksforgeeks.org/newton-forward-backward-interpolation/
+from __future__ import annotations
 
 import math
-from typing import List
 
 
 # for calculating u value
@@ -22,7 +22,7 @@ def ucal(u: float, p: int) -> float:
 
 def main() -> None:
     n = int(input("enter the numbers of values: "))
-    y: List[List[float]] = []
+    y: list[list[float]] = []
     for i in range(n):
         y.append([])
     for i in range(n):