### Apache Airflow version

2.5.1

### What happened

/calendar page give a problem, here is the capture



![屏幕截图 2023-01-30 093116](https://user-images.githubusercontent.com/19165258/215369479-9fc7de5c-f190-460c-9cf7-9ab27d8ac355.png)


### What you think should happen instead

_No response_

### How to reproduce

_No response_

### Operating System

Ubuntu 22.04.1 LTS

### Versions of Apache Airflow Providers

Distributor ID: Ubuntu
Description:    Ubuntu 22.04.1 LTS
Release:        22.04
Codename:       jammy

### Deployment

Other

### Deployment details


Distributor ID: Ubuntu
Description:    Ubuntu 22.04.1 LTS
Release:        22.04
Codename:       jammy

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

return self._set_notification_property(items, "email_sent", True)
    @action(
        "mulemailsentfalse",
        "Set email sent to false",
        "Are you sure you want to mark these SLA alerts as emails not sent yet?",
        single=False,
    )
    def action_mulemailsentfalse(self, items: list[SlaMiss]):
        return self._set_notification_property(items, "email_sent", False)
    @provide_session
    def _set_notification_property(self, items: list[SlaMiss], attr: str, new_value: bool, session=None):
        try:
            count = 0
            for sla in items:
                count += 1
                setattr(sla, attr, new_value)
                session.merge(sla)
            session.commit()
            flash(f"{count} SLAMisses had {attr} set to {new_value}.")
        except Exception as ex:
            flash(str(ex), "error")
            flash("Failed to set state", "error")
        self.update_redirect()
        return redirect(self.get_default_url())