[Tests] Standardize RNG seed utility across test files (#32982)

Signed-off-by: 7. Sun <jhao.sun@gmail.com>

vllm/utils/torch_utils.py

@@ -333,6 +333,8 @@ def set_random_seed(seed: int | None) -> None:
         random.seed(seed)
         np.random.seed(seed)
         torch.manual_seed(seed)
+        if torch.cuda.is_available():
+            torch.cuda.manual_seed_all(seed)
 
 
 def create_kv_caches_with_random_flash(