fix: Don't allow negative amount on Payment Request #41905 (backport #41959)

[mergify]

---

This is an automatic backport of pull request #41959 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of b823aa6 has failed:

On branch mergify/bp/version-15-hotfix/pr-41959
Your branch is up to date with 'origin/version-15-hotfix'.

You are currently cherry-picking commit b823aa66bf.
  (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/accounts/doctype/payment_request/payment_request.json

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

[frappe-pr-bot]

🎉 This issue has been resolved in version 15.31.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀