fix warning log for Transformer SD3 (#8496)

fix warning log

src/diffusers/models/transformers/transformer_sd3.py

@@ -282,9 +282,10 @@ class SD3Transformer2DModel(ModelMixin, ConfigMixin, PeftAdapterMixin, FromOrigi
             # weight the lora layers by setting `lora_scale` for each PEFT layer
             scale_lora_layers(self, lora_scale)
         else:
-            logger.warning(
-                "Passing `scale` via `joint_attention_kwargs` when not using the PEFT backend is ineffective."
-            )
+            if joint_attention_kwargs is not None and joint_attention_kwargs.get("scale", None) is not None:
+                logger.warning(
+                    "Passing `scale` via `joint_attention_kwargs` when not using the PEFT backend is ineffective."
+                )
 
         height, width = hidden_states.shape[-2:]