Fix bench_serving does not support changing warmup requests (#6439)

python/sglang/bench_serving.py

@@ -1618,6 +1618,7 @@ def run_benchmark(args_: argparse.Namespace):
             profile=args.profile,
             pd_separated=args.pd_separated,
             flush_cache=args.flush_cache,
+            warmup_requests=args.warmup_requests,
         )
     )