fix: 邮件主题前缀设置不生效的问题

apps/notifications/backends/email.py

@@ -11,6 +11,7 @@ class Email(BackendBase):
     def send_msg(self, users, message, subject):
         from_email = settings.EMAIL_FROM or settings.EMAIL_HOST_USER
         accounts, __, __ = self.get_accounts(users)
+        subject = (settings.EMAIL_SUBJECT_PREFIX or '') + subject
         send_mail(subject, message, from_email, accounts, html_message=message)