[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

data_structures/heap/fibonacci_heap.py

@@ -162,4 +162,4 @@ def merge(self, other):
             self.min_node = other.min_node
 
         self.total_nodes += other.total_nodes
-        return self
+        return self