fix: add currency in options for rate field in pricing rule (backport #43239)

[mergify]

Issue:
Not showing appropriate currency symbol in rate field in pricing rule list view
https://support.frappe.io/helpdesk/tickets/22014

Before fix:

After fix:

Backport needed:
v15

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This is an automatic backport of pull request #43239 done by Mergify.

[mergify]

Cherry-pick of 636c013 has failed:

On branch mergify/bp/version-15-hotfix/pr-43239
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Unmerged paths:
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	both modified:   erpnext/accounts/doctype/pricing_rule/pricing_rule.json

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