fix(migration): resolve breaking issue in migrate_shift_assignment_schedule_to_shift_schedule.py

[abdussamadbello]

Pull Request Description

Target Branch

Target branch: version-15 (or appropriate branch for the fix)

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Summary

This PR updates the migrate_shift_assignment_schedule_to_shift_schedule.py script to resolve breaking migration issues in version 15 of ERPNext.

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Details

• Issue Addressed: The migration script for Shift Assignment Schedule caused errors during migration when the related DocType or table was missing in the database.
• Solution: The updated script adds error handling to gracefully handle missing DocTypes or records. Instead of breaking the migration, errors are logged, and processing continues for valid data.
• Business Logic: All changes are compliant with the server-side business logic guidelines.
• Tests: Local testing confirmed the script no longer interrupts migration while preserving intended functionality.

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Checklist

• PR follows the [commit message convention](http://karma-runner.github.io/4.0/dev/git-commit-msg.html).
• Tests pass locally, including migration and database operations.
• Business logic remains server-side and adheres to project standards.
• Documentation updated where necessary.
• Closes the reported migration issue: closes #2558.

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References

• [Documentation Guidelines](https://github.com/frappe/erpnext/wiki/Page-format-for-ERPNext-docs)
• [Contribution Guide](https://github.com/frappe/erpnext/wiki/Contribution-Guidelines)
• [Pull Request Checklist](https://github.com/frappe/erpnext/wiki/Pull-Request-Checklist)

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Closes

Closes 2558

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Let me know if additional details or adjustments are needed!

[abdussamadbello]

@krantheman cfb5c85 . This is a fix to the update you made on shift assignment schedule thats breaking the migration

[ruchamahabal]

Fixed with #2571. Closing