typing: Import StrPromise alias from django_stubs_ext.

This saves us from using a conditional import.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

zerver/actions/message_edit.py

@@ -1,5 +1,5 @@
 import datetime
-from typing import TYPE_CHECKING, Any, Dict, Iterable, List, Optional, Set
+from typing import Any, Dict, Iterable, List, Optional, Set
 
 from django.conf import settings
 from django.db import transaction
@@ -8,6 +8,7 @@ from django.utils.timezone import now as timezone_now
 from django.utils.translation import gettext as _
 from django.utils.translation import gettext_lazy
 from django.utils.translation import override as override_language
+from django_stubs_ext import StrPromise
 
 from zerver.actions.message_delete import DeleteMessagesEvent
 from zerver.actions.message_flags import do_update_mobile_push_notification
@@ -65,9 +66,6 @@ from zerver.models import (
 )
 from zerver.tornado.django_api import send_event
 
-if TYPE_CHECKING:
-    from django.utils.functional import _StrPromise as StrPromise
-
 
 def subscriber_info(user_id: int) -> Dict[str, Any]:
     return {"id": user_id, "flags": ["read"]}
@@ -200,10 +198,10 @@ def send_message_moved_breadcrumbs(
     user_profile: UserProfile,
     old_stream: Stream,
     old_topic: str,
-    old_thread_notification_string: Optional["StrPromise"],
+    old_thread_notification_string: Optional[StrPromise],
     new_stream: Stream,
     new_topic: Optional[str],
-    new_thread_notification_string: Optional["StrPromise"],
+    new_thread_notification_string: Optional[StrPromise],
     changed_messages_count: int,
 ) -> None:
     # Since moving content between streams is highly disruptive,