fix compatibility problem caused by tool node attribute 'tool_node_version' judgement error (#26274)

api/core/workflow/nodes/agent/agent_node.py

                         # But for backward compatibility with historical data
                         # this version field judgment is still preserved here.
                         runtime_variable_pool: VariablePool | None = None
-                        if node_data.version != "1" or node_data.tool_node_version != "1":
+                        if node_data.version != "1" or node_data.tool_node_version is not None:
                             runtime_variable_pool = variable_pool
                         tool_runtime = ToolManager.get_agent_tool_runtime(
                             self.tenant_id, self.app_id, entity, self.invoke_from, runtime_variable_pool

api/core/workflow/nodes/tool/tool_node.py

             # But for backward compatibility with historical data
             # this version field judgment is still preserved here.
             variable_pool: VariablePool | None = None
-            if node_data.version != "1" or node_data.tool_node_version != "1":
+            if node_data.version != "1" or node_data.tool_node_version is not None:
                 variable_pool = self.graph_runtime_state.variable_pool
             tool_runtime = ToolManager.get_workflow_tool_runtime(
                 self.tenant_id, self.app_id, self._node_id, self._node_data, self.invoke_from, variable_pool