[mypy] Add/fix type annotations for quick_sort(#4085) (#4215)

Co-authored-by: goodm2 <4qjpngu8mem8cz>

sorts/quick_sort.py

@@ -7,6 +7,7 @@ python3 -m doctest -v quick_sort.py
 For manual testing run:
 python3 quick_sort.py
 """
+from typing import List
 
 
 def quick_sort(collection: list) -> list:
@@ -26,8 +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 = []  # All elements greater than pivot
-    lesser = []  # 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)