[Bugfix] Weight loading fix for OPT model (#9042)

Co-authored-by: dvres <dvres@fri.uni-lj.si>

vllm/model_executor/models/opt.py

@@ -353,7 +353,7 @@ class OPTForCausalLM(nn.Module):
         ]
         params_dict = dict(self.named_parameters(remove_duplicate=False))
         for name, loaded_weight in weights:
-            if "lm_head.weight" in name:
+            if "lm_head.weight" in name and self.config.tie_word_embeddings:
                 continue
             if name.startswith("decoder."):
                 name = "model." + name