Fix executor validation error referencing non-existent [core] executors (apache#71336)

`_validate_executor_fields` raised UnknownExecutorException telling users
to check their "[core] executors configuration" when a task's executor
isn't available. That config key doesn't exist -- Airflow has a single
[core] executor key (conf.get_mandatory_value("core", "executor")),
which accepts a comma-separated list to configure multiple executors.
The plural "executors" only ever appears in this error text, sending
users looking for a setting that isn't there.

Fixes both branches of the message (with and without a team name).

Author: roshanprabu

airflow-core/src/airflow/dag_processing/dagbag.py

@@ -151,12 +151,12 @@ def _validate_executor_fields(dag: DAG, bundle_name: str | None = None) -> None:
                     f"Task '{task.task_id}' specifies executor '{task.executor}', which is not available "
                     f"for team '{dag_team_name}' (the team associated with DAG '{dag.dag_id}') or as a global executor. "
                     f"Make sure '{task.executor}' is configured for team '{dag_team_name}' or globally in your "
-                    "[core] executors configuration, or update the task's executor to use one of the "
+                    "[core] executor configuration, or update the task's executor to use one of the "
                     f"configured executors for team '{dag_team_name}' or available global executors."
                 )
             raise UnknownExecutorException(
                 f"Task '{task.task_id}' specifies executor '{task.executor}', which is not available. "
-                "Make sure it is listed in your [core] executors configuration, or update the task's "
+                "Make sure it is listed in your [core] executor configuration, or update the task's "
                 "executor to use one of the configured executors."
             )
 

airflow-core/tests/unit/dag_processing/test_dagbag.py

@@ -185,7 +185,7 @@ def test_executor_validation_failure_with_team(self, mock_lookup, mock_manager_c
                     "Task 'task1' specifies executor 'invalid.executor', which is not available "
                     "for team 'test_team' (the team associated with DAG 'test-dag') or as a global executor. "
                     "Make sure 'invalid.executor' is configured for team 'test_team' or globally in your "
-                    "[core] executors configuration, or update the task's executor to use one of the "
+                    "[core] executor configuration, or update the task's executor to use one of the "
                     "configured executors for team 'test_team' or available global executors."
                 ),
             ):
@@ -204,7 +204,7 @@ def test_executor_validation_failure_no_team(self, mock_lookup):
                 UnknownExecutorException,
                 match=re.escape(
                     "Task 'task1' specifies executor 'invalid.executor', which is not available. "
-                    "Make sure it is listed in your [core] executors configuration, or update the task's "
+                    "Make sure it is listed in your [core] executor configuration, or update the task's "
                     "executor to use one of the configured executors."
                 ),
             ):
@@ -258,7 +258,7 @@ def test_global_executor_fallback_failure(self, mock_lookup, mock_manager_class)
                     "Task 'task1' specifies executor 'unknown.executor', which is not available "
                     "for team 'test_team' (the team associated with DAG 'test-dag') or as a global executor. "
                     "Make sure 'unknown.executor' is configured for team 'test_team' or globally in your "
-                    "[core] executors configuration, or update the task's executor to use one of the "
+                    "[core] executor configuration, or update the task's executor to use one of the "
                     "configured executors for team 'test_team' or available global executors."
                 ),
             ):
@@ -330,7 +330,7 @@ def test_validate_executor_field_executor_not_configured():
         UnknownExecutorException,
         match=re.escape(
             "Task 't1' specifies executor 'test.custom.executor', which is not available. "
-            "Make sure it is listed in your [core] executors configuration, or update the task's "
+            "Make sure it is listed in your [core] executor configuration, or update the task's "
             "executor to use one of the configured executors."
         ),
     ):