docs: update 3-3-approval-workflows.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟢 high

What changed

Added a "Good to know" callout under Approval Nodes explaining that a node with no eligible active approver now causes submissions (e.g. credit notes) to be rejected with a clear error instead of hanging indefinitely, plus a corresponding Best Practices bullet about keeping approvers active.

Source PRs

• light#7541 — feat(GREEN-1926): fail loudly on unsatisfiable approval chains

How to use this PR

1. Review the diff against the existing article — focus on accuracy and customer voice.
2. Merge if it reads well. Edit and push to this branch if it needs adjustment.
3. Close without merging if the article doesn't actually need this update.

Once we have a track record of clean drafts, we'll graduate to auto-merge with a delay buffer. For now: human-in-the-loop.