[@mantine/core] fix: prevent onClose trigger on escape when modal is not open

[hsskey]

Fix: Ensure onClose is not triggered by escape key when Modal is not open

This PR addresses a specific issue where the onClose function of the Modal component was incorrectly triggered by pressing the Escape key, even when the Modal was not actively open.

Problem:
When the Escape key was pressed, the onClose handler was executed regardless of the Modal's open state. This could unintentionally disrupt the user experience and application state if the onClose logic was not meant to be executed at that time.

Solution:
The fix involves a simple, yet effective modification in the useModal hook. By adding a conditional check that ensures the Modal is open (opened state is true) before invoking the onClose function, we prevent unwanted side effects

fixes #6148
commit: b6ea042

[rtivital]

Thanks!