fix(holiday-list): use same date format for same holiday error message (backport #42606)

[mergify]

Fix frappe/hrms#1847

Please provide enough information so that others can review your pull request:

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

Before:

After:

---

This is an automatic backport of pull request #42606 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a435441 has failed:

On branch mergify/bp/version-14-hotfix/pr-42606
Your branch is up to date with 'origin/version-14-hotfix'.

You are currently cherry-picking commit a435441536.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   erpnext/setup/doctype/holiday_list/holiday_list.py

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally