CDatePicker: clicking on nav triggers a form submit

Version: 5.15.0. Not tested on other versions

Clicking on CDatePicker's nav arrows and the year triggers a form submission:

<img width="347" height="353" alt="Image" src="https://github.com/user-attachments/assets/0c95dc6a-818c-4cd9-a4be-c2bd5631c8e0" />

