typing: Import ValuesQuerySet alias from django_stubs_ext.

This saves us from using a conditional import.

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

zerver/lib/cache_helpers.py

@@ -1,12 +1,13 @@
 # See https://zulip.readthedocs.io/en/latest/subsystems/caching.html for docs
 import datetime
 import logging
-from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, Tuple
+from typing import Any, Callable, Dict, Iterable, Tuple
 
 from django.conf import settings
 from django.contrib.sessions.models import Session
 from django.db.models.query import QuerySet
 from django.utils.timezone import now as timezone_now
+from django_stubs_ext import ValuesQuerySet
 
 # This file needs to be different from cache.py because cache.py
 # cannot import anything from zerver.models or we'd have an import
@@ -32,9 +33,6 @@ from zerver.models import (
     huddle_hash_cache_key,
 )
 
-if TYPE_CHECKING:
-    from django.db.models.query import _QuerySet as ValuesQuerySet
-
 
 def user_cache_items(
     items_for_remote_cache: Dict[str, Tuple[UserProfile]], user_profile: UserProfile
@@ -73,7 +71,7 @@ def session_cache_items(
     items_for_remote_cache[store.cache_key] = store.decode(session.session_data)
 
 
-def get_active_realm_ids() -> "ValuesQuerySet[RealmCount, int]":
+def get_active_realm_ids() -> ValuesQuerySet[RealmCount, int]:
     """For installations like Zulip Cloud hosting a lot of realms, it only makes
     sense to do cache-filling work for realms that have any currently
     active users/clients.  Otherwise, we end up with every single-user