[Bugfix] Fix two batch overlap with auto DeepEP Dispatch (#7853)

Signed-off-by: Shangming Cai <caishangming@linux.alibaba.com>

python/sglang/srt/two_batch_overlap.py

@@ -490,6 +490,7 @@ class TboForwardBatchPreparer:
         output_dict["spec_info"] = output_spec_info
         for key in [
             "forward_mode",
+            "is_extend_in_batch",
             "return_logprob",
             "req_to_token_pool",
             "token_to_kv_pool",