Don'e assume position_embedding_type will be present for BERT and RoBERTa models (#30770)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/model_executor/models/bert.py

@@ -55,7 +55,9 @@ class BertEmbedding(nn.Module):
             "position_ids",
             torch.arange(config.max_position_embeddings).unsqueeze(0),
         )
-        self.position_embedding_type = config.position_embedding_type
+        self.position_embedding_type = getattr(
+            config, "position_embedding_type", "absolute"
+        )
         if self.position_embedding_type != "absolute":
             raise ValueError(
                 "Only 'absolute' position_embedding_type" + " is supported"