fix: Earned Leave allocation based on joining date fixes (backport #29711)

[mergify]

This is an automatic backport of pull request #29711 done by Mergify.
Cherry-pick of c7be9ef has failed:

On branch mergify/bp/version-13-hotfix/pr-29711
Your branch is ahead of 'origin/version-13-hotfix' by 2 commits.
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You are currently cherry-picking commit c7be9ef5d2.
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Unmerged paths:
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	both modified:   erpnext/hr/doctype/leave_policy_assignment/leave_policy_assignment.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/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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