### 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)

"""Import variables"""
        try:
            variable_dict = json.loads(request.files["file"].read())
        except Exception:
            self.update_redirect()
            flash("Missing file or syntax error.", "error")
            return redirect(self.get_redirect())
        else:
            suc_count = fail_count = 0
            for k, v in variable_dict.items():
                try:
                    models.Variable.set(k, v, serialize_json=not isinstance(v, str))
                except Exception as e:
                    logging.info("Variable import failed: %s", repr(e))
                    fail_count += 1
                else:
                    suc_count += 1
            flash(f"{suc_count} variable(s) successfully updated.")
            if fail_count:
                flash(f"{fail_count} variable(s) failed to be updated.", "error")
            self.update_redirect()
            return redirect(self.get_redirect())
class JobModelView(AirflowModelView):
    """View to show records from Job table"""