fix: posting_time issue (backport #44870)

[mergify]

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This is an automatic backport of pull request #44870 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 079b860 has failed:

On branch mergify/bp/version-15-hotfix/pr-44870
Your branch is up to date with 'origin/version-15-hotfix'.

You are currently cherry-picking commit 079b86044e.
  (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)

Changes to be committed:
	modified:   erpnext/stock/serial_batch_bundle.py

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

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