fix: change CronTrigger next_fire start time (#1718)

Replaces the croniter start_time in CronTrigger from `datetime.now()` to `self.last_call_time.astimezone()` to fix a bug causing possible multiple firing.

Fixes #1717

Author: mifuyutsuki

interactions/models/internal/tasks/triggers.py

@@ -163,4 +163,4 @@ def __init__(self, cron: str, tz: "_TzInfo" = timezone.utc) -> None:
         self.tz = tz
 
     def next_fire(self) -> datetime | None:
-        return croniter(self.cron, datetime.now(tz=self.tz)).next(datetime)
+        return croniter(self.cron, self.last_call_time.astimezone(self.tz)).next(datetime)