[Bugfix] fix detokenizer shallow copy (vllm-project#5919)

Signed-off-by: Alvant <[email protected]>

vllm/transformers_utils/detokenizer.py

@@ -90,7 +90,7 @@ def decode_prompt_logprobs_inplace(self, seq_group: SequenceGroup,
             prefix_offset = next_iter_prefix_offset
             read_offset = next_iter_read_offset
             if prev_tokens is None:
-                prev_tokens = next_iter_tokens
+                prev_tokens = next_iter_tokens.copy()
             else:
                 prev_tokens.extend(next_iter_tokens)