[Misc] Replace Optional[X] with X | None syntax (#33332)

Signed-off-by: carlory <baofa.fan@daocloud.io>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

vllm/platforms/rocm.py

@@ -3,7 +3,7 @@
 
 import os
 from functools import cache, lru_cache, wraps
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING
 
 import torch
 
@@ -356,7 +356,7 @@ class RocmPlatform(Platform):
         cls,
         head_size: int,
         dtype: torch.dtype,
-        backend: Optional["AttentionBackendEnum"] = None,
+        backend: "AttentionBackendEnum | None" = None,
     ) -> "AttentionBackendEnum":
         if backend is not None:
             assert backend in cls.get_supported_vit_attn_backends(), (