fix: check for correct holiday list used in leave application

[meike289]

Describe your changes

This PR checks for the correct holiday list in leave ledger entries for a correct calculation.

Checklist

• Import latest production database dump
• Install the leave_calendar app
• Access {site}.localhost:8000/leave_calendar
• Verify that the calculated leave balances (left columns) match expected values
• Confirm that discrepancies caused by changes in working schedules (e.g., switching from a 4-day to a 5-day week in the same year) are correctly handled
• Ensure that previously incorrect leave day calculations are now resolved
• Code changes are transparent and well-documented
• Coding standards are followed