Improve get dag grid structure endpoint speed (apache#55942)

* Improve get dag structure endpoint speed


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Co-authored-by: Elad Kalif <45845474+eladkal@users.noreply.github.com>

Author: dor-bernstein

airflow-core/src/airflow/api_fastapi/core_api/routes/ui/grid.py

@@ -162,6 +162,7 @@ def get_dag_structure(
 
     serdags = session.scalars(
         select(SerializedDagModel).where(
+            SerializedDagModel.dag_id == dag_id,
             SerializedDagModel.dag_version_id.in_(
                 select(TaskInstance.dag_version_id)
                 .join(TaskInstance.dag_run)