address greptile review feedback (greploop iteration 8)

- Persist normalized (tz-aware) expires_at in PATCH path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

litellm/proxy/scheduled_tasks/endpoints.py

@@ -341,6 +341,7 @@ async def update_scheduled_task(
             raise HTTPException(
                 status_code=400, detail="expires_at must be in the future"
             )
+        fields["expires_at"] = new_expires
 
     try:
         row = await store.update_task_for_owner(