fix: update default KSA VAT rate for setup (backport #27614)

[mergify]

VAT rate in KSA was updated by the government from 5% to 15%. ERPNext still sets it up at 5% to date.

source:

https://taxsummaries.pwc.com/saudi-arabia/corporate/other-taxes

https://www2.deloitte.com/ly/en/pages/tax/articles/ksa-vat-rate-increase-15percent-1-july-2020.html

This PR updates the standard/default VAT to 15%.

EDIT: can be backported to v13 and v12.

no-docs

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This is an automatic backport of pull request #27614 done by Mergify.

[mergify]

Cherry-pick of abded89 has failed:

On branch mergify/bp/version-13-hotfix/pr-27614
Your branch is up to date with 'origin/version-13-hotfix'.

You are currently cherry-picking commit abded895f3.
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Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   erpnext/setup/setup_wizard/data/country_wise_tax.json

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