fix: Fix API endpoint for Frankfurter (backport #43476)

[mergify]

Frankfurter just passed a breaking change which breaks the "frankfurter.app" endpoint for API calls. The new endpoint is "api.frankfurter.app".

re: #43472

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This is an automatic backport of pull request #43476 done by Mergify.

[mergify]

Cherry-pick of 33e7211 has failed:

On branch mergify/bp/version-13-hotfix/pr-43476
Your branch is up to date with 'origin/version-13-hotfix'.

You are currently cherry-picking commit 33e72111c7.
  (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)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   erpnext/accounts/doctype/currency_exchange_settings/currency_exchange_settings.py
	both modified:   erpnext/setup/install.py

no changes added to commit (use "git add" and/or "git commit -a")

Cherry-pick of c444de0 has failed:

On branch mergify/bp/version-13-hotfix/pr-43476
Your branch is ahead of 'origin/version-13-hotfix' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit c444de017a.
  (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)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   erpnext/setup/doctype/currency_exchange/test_currency_exchange.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/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[sagarvora]

nothing to merge, so closed.