Fix http exception when ti not found for extra links API (#51443)

* Fix http exception when ti not found for extra links API

* no question of dagrun here, remove that test

Author: amoghrajesh

airflow-core/src/airflow/api_fastapi/core_api/routes/public/extra_links.py

@@ -77,7 +77,7 @@ def get_extra_links(
     if not ti:
         raise HTTPException(
             status.HTTP_404_NOT_FOUND,
-            f"DAG Run with ID = {dag_run_id} not found",
+            "TaskInstance not found",
         )
 
     all_extra_link_pairs = (

airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_extra_links.py

@@ -131,12 +131,6 @@ def _create_dag(self, dag_maker):
                 {"detail": "DAG with ID = INVALID not found"},
                 id="missing_dag",
             ),
-            pytest.param(
-                "/dags/TEST_DAG_ID/dagRuns/INVALID/taskInstances/TEST_SINGLE_LINK/links",
-                404,
-                {"detail": "DAG Run with ID = INVALID not found"},
-                id="missing_dag_run",
-            ),
             pytest.param(
                 "/dags/TEST_DAG_ID/dagRuns/TEST_DAG_RUN_ID/taskInstances/INVALID/links",
                 404,