Fix: use data.type instead of type when checking datasource node (#25965)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/services/rag_pipeline/rag_pipeline.py

         datasource_nodes = workflow.graph_dict.get("nodes", [])
         datasource_plugins = []
         for datasource_node in datasource_nodes:
-            if datasource_node.get("type") == "datasource":
-                datasource_node_data = datasource_node.get("data", {})
+            if datasource_node.get("data", {}).get("type") == "datasource":
+                datasource_node_data = datasource_node["data"]
                 if not datasource_node_data:
                     continue