### Apache Airflow version

2.4.2

### What happened

Create a DAG and set the schedule parameter using a CronTriggerTimeTable instance. Enable the DAG so that there is DAG run data. Try to access the Calendar View for the DAG. An ERR_EMPTY_RESPONSE error is displayed instead of the page.

The Calendar View is accessible for other DAGs  that are using the schedule_interval set to a cron string instead.

### What you think should happen instead

The Calendar View should have been displayed.

### How to reproduce

Create a DAG and set the schedule parameter to a CronTriggerTimeTable instance. Enable the DAG and allow some DAG runs to occur. Try to access the Calender View for the DAG.

### Operating System

Red Hat Enterprise Linux 8.6

### Versions of Apache Airflow Providers

_No response_

### Deployment

Virtualenv installation

### Deployment details

Airflow 2.4.2 installed via pip with Python3.9 to venv using constraints.

### Anything else

_No response_

### Are you willing to submit PR?

- [X] 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)

"""View to show records from Variable table"""
    route_base = "/variable"
    list_template = "airflow/variable_list.html"
    edit_template = "airflow/variable_edit.html"
    show_template = "airflow/variable_show.html"
    show_widget = AirflowVariableShowWidget
    datamodel = AirflowModelView.CustomSQLAInterface(models.Variable)  
    class_permission_name = permissions.RESOURCE_VARIABLE
    method_permission_name = {
        "add": "create",
        "list": "read",
        "edit": "edit",
        "show": "read",
        "delete": "delete",
        "action_muldelete": "delete",