Unconditionally disable start_from_trigger (apache#53744)

Author: uranusjr

airflow-core/src/airflow/models/mappedoperator.py

@@ -72,13 +72,18 @@ def expand_start_from_trigger(self, *, context: Context, session: Session) -> bo
 
         :meta private:
         """
-        if not self.partial_kwargs.get("start_from_trigger", self.start_from_trigger):
+        if self.partial_kwargs.get("start_from_trigger", self.start_from_trigger):
             log.warning(
                 "Starting a mapped task from triggerer is currently unsupported",
                 task_id=self.task_id,
                 dag_id=self.dag_id,
             )
-            return False
+
+        # This is intentional. start_from_trigger does not work correctly with
+        # sdk-db separation yet, so it is disabled unconditionally for now.
+        # TODO: TaskSDK: Implement this properly.
+        return False
+
         # start_from_trigger only makes sense when start_trigger_args exists.
         if not self.start_trigger_args:
             return False