[Fix] Keep scheduler.running as deque (#2523)

Author: njhill

vllm/core/scheduler.py

@@ -332,10 +332,8 @@ def free_seq(self, seq: Sequence) -> None:
         self.block_manager.free(seq)
 
     def free_finished_seq_groups(self) -> None:
-        self.running = [
-            seq_group for seq_group in self.running
-            if not seq_group.is_finished()
-        ]
+        self.running = deque(seq_group for seq_group in self.running
+                             if not seq_group.is_finished())
 
     def _allocate(self, seq_group: SequenceGroup) -> None:
         self.block_manager.allocate(seq_group)