Fix `--gen_kwargs` and VLLM (`temperature` not respected) (#1800)

* Update vllm_causallms.py

* adjust

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Co-authored-by: lintangsutawika <lintang@eleuther.ai>

lm_eval/models/vllm_causallms.py

@@ -499,7 +499,10 @@ class VLLM(TemplateLM):
     def modify_gen_kwargs(kwargs: dict) -> dict:
         # sampling_params
         do_sample = kwargs.pop("do_sample", None)
-        if do_sample is False or "temperature" not in kwargs:
+        if do_sample is False and "temperature" not in kwargs:
+            eval_logger.debug(
+                "Got `do_sample=False` and no temperature value, setting VLLM temperature to 0.0 ..."
+            )
             kwargs["temperature"] = 0.0
         # hf defaults
         kwargs["skip_special_tokens"] = kwargs.get("skip_special_tokens", False)