Fix bug in setting until kwarg in openai completions (#1784)

lm_eval/models/openai_completions.py

@@ -430,7 +430,7 @@ class OpenaiChatCompletionsLM(LM):
                     if "until" in kwargs.keys():
                         until = kwargs.pop("until")
                         if isinstance(until, str):
-                            until = [kwargs]
+                            until = [until]
                         elif not isinstance(until, list):
                             raise ValueError(
                                 f"Expected repr(kwargs['until']) to be of type Union[str, list] but got {until}"