[Misc] Modify LRUCache touch (#16689)

Signed-off-by: Jee Jee Li <[email protected]>

Author: jeejeelee

vllm/utils.py

@@ -316,7 +316,10 @@ def stat(self, *, delta: bool = False) -> CacheInfo:
         return info
 
     def touch(self, key: _K) -> None:
-        self._LRUCache__update(key)  # type: ignore
+        try:
+            self._LRUCache__order.move_to_end(key)  # type: ignore
+        except KeyError:
+            self._LRUCache__order[key] = None  # type: ignore
 
     @overload
     def get(self, key: _K, /) -> Optional[_V]: