Disable starting a mapped task from trigger (apache#48006)

The scheduler versions of "ExpandInput" classes don't have a "resolve" method anymore so scheduler crashes when trying to expand_start_from_trigger.  To keep the scheduler running, for now we disable the feature.

Related to apache#47735

May be fixed in apache#48009

Author: dstandish

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

@@ -20,6 +20,7 @@
 from typing import TYPE_CHECKING
 
 import attrs
+import structlog
 
 from airflow.models.abstractoperator import AbstractOperator
 from airflow.sdk.definitions.mappedoperator import MappedOperator as TaskSDKMappedOperator
@@ -31,6 +32,8 @@
 
     from airflow.sdk.definitions.context import Context
 
+log = structlog.get_logger()
+
 
 @attrs.define(
     kw_only=True,
@@ -57,6 +60,13 @@ def expand_start_from_trigger(self, *, context: Context, session: Session) -> bo
 
         :meta private:
         """
+        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
         # start_from_trigger only makes sense when start_trigger_args exists.
         if not self.start_trigger_args:
             return False