style: move the SchedulerExpandInput into type checking block

Author: Lee-W

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

@@ -20,7 +20,7 @@
 import functools
 import operator
 from collections.abc import Iterable, Sized
-from typing import TYPE_CHECKING, Any, ClassVar, Union
+from typing import TYPE_CHECKING, Any, ClassVar
 
 import attrs
 
@@ -138,7 +138,8 @@ def get_total_map_length(self, run_id: str, *, session: Session) -> int:
     "list-of-dicts": SchedulerListOfDictsExpandInput,
 }
 
-SchedulerExpandInput = Union[SchedulerDictOfListsExpandInput, SchedulerListOfDictsExpandInput]
+if TYPE_CHECKING:
+    SchedulerExpandInput = SchedulerDictOfListsExpandInput | SchedulerListOfDictsExpandInput
 
 
 def create_expand_input(kind: str, value: Any) -> SchedulerExpandInput: