fix(holiday-list): use same date format for same holiday error message

[ananyo141]

Fix frappe/hrms#1847

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Fixes the issue where the date format in the error message doesn't adhere to the system settings for the date format.

Explain the details for making this change. What existing problem does the pull request solve?

The new patch uses the default system format for the error message too.

Screenshots/GIFs

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After: