Raise ``TaskAlreadyRunningError`` when starting an already-running task instance (#60855)

* Fix task marked as failed on executor redelivery

Handle 409 CONFLICT (task already running) from the API server gracefully
by raising TaskAlreadyRunningError instead of letting it propagate as a
generic failure.

closes: #58441

* Fix test_get_not_found assertion to match unwrapped detail format

* address review feed back

* Trigger CI re-run

* Trigger CI re-run