fix: add doctest.testmod() to gnome_sort.py (TheAlgorithms#15023)

Co-authored-by: deepshekhardas <deepshekharadas1234@gmail.com>

Author: deepshekhardas

sorts/gnome_sort.py

@@ -51,6 +51,9 @@ def gnome_sort(lst: list) -> list:
 
 
 if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
     user_input = input("Enter numbers separated by a comma:\n").strip()
     unsorted = [int(item) for item in user_input.split(",")]
     print(gnome_sort(unsorted))