fixed mypy issue

Signed-off-by: Arya Pratap Singh <notaryasingh@gmail.com>

Author: ARYPROGRAMMER

data_structures/heap/fibonacci_heap.py

@@ -84,6 +84,8 @@ def insert(self, key: Any, value: Any = None) -> None:
             node.right = node
         else:
             # Insert into root list
+            assert self.min_node.right is not None
+            assert self.min_node.left is not None
             node.left = self.min_node
             node.right = self.min_node.right
             self.min_node.right.left = node