refactor: Made task optional again in BaseTrigger

Author: dabla

airflow-core/src/airflow/triggers/base.py

@@ -90,8 +90,10 @@ def _set_context(self, context):
         pass
 
     @property
-    def task(self) -> Operator:
-        return self.task_instance.task
+    def task(self) -> Operator | None:
+        if self.task_instance:
+            return self.task_instance.task
+        return None
 
     @property
     def task_instance(self) -> TaskInstance | None: