[`Pix2Struct`] Fix pix2struct cross attention (#25200)

* fix pix2struct cross attention

* fix torchscript slow test

src/transformers/models/pix2struct/modeling_pix2struct.py

@@ -1547,8 +1547,9 @@ class Pix2StructTextModel(Pix2StructPreTrainedModel):
                 present_key_value_states = present_key_value_states + (present_key_value_state,)
 
             if output_attentions:
-                all_attentions = all_attentions + (layer_outputs[2],)
-                all_cross_attentions = all_cross_attentions + (layer_outputs[3],)
+                all_attentions = all_attentions + (layer_outputs[3],)
+                if encoder_hidden_states is not None:
+                    all_cross_attentions = all_cross_attentions + (layer_outputs[5],)
 
         hidden_states = self.final_layer_norm(hidden_states)
         hidden_states = self.dropout(hidden_states)