fix: last purchase rate for purchase invoice (backport #43448)

[mergify]

1. Create the Purchase Invoice with rate as 200, the last purchase rate in the item master set as 200
2. Create the Purchase Invoice with rate as 300, the last purchase rate in the item master set as 300
3. Cancel the second purchase invoice, the last purchase rate in the item master should be 200 but it's showing the rate as 300

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This is an automatic backport of pull request #43448 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of fb9d106 has failed:

On branch mergify/bp/version-14-hotfix/pr-43448
Your branch is up to date with 'origin/version-14-hotfix'.

You are currently cherry-picking commit fb9d106633.
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Changes to be committed:
	modified:   erpnext/controllers/buying_controller.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   erpnext/accounts/doctype/purchase_invoice/test_purchase_invoice.py
	both modified:   erpnext/public/js/controllers/transaction.js
	both modified:   erpnext/stock/doctype/item/item.py

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