Update dynamic_programming/fibonacci.py

Co-authored-by: Bertrand Awenze <156874668+bertrand-awz@users.noreply.github.com>

Author: Achintya47

dynamic_programming/fibonacci.py

@@ -96,7 +96,8 @@ def get(self, index: int) -> list[int]:
             True
         """
         if index < 0:
-            raise ValueError(f"Index must be non-negative, got {index}")
+            error_msg = f"Index must be non-negative, got {index}"
+            raise ValueError(error_msg)
 
         if index == 0:
             return []