[CLEAN] Synthetic Benchmark PR #30251 - fix: workflow incorrectly marked as completed while nodes are still executing

[tomerqodo]

Benchmark PR langgenius#30251

Type: Clean (correct implementation)

Original PR Title: fix: workflow incorrectly marked as completed while nodes are still executing
Original PR Description:

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Fixes langgenius#30195
Fixes langgenius#29316

Summary

When the last upstream node is skipped, the downstream node is added only to _ready_queue and not to _executing_nodes.
After the worker thread consumes _ready_queue, both _ready_queue and _executing_nodes become empty.
As a result, the _dispatcher_loop exits the while loop incorrectly.

Can reproduct use thie DSL: CheckSkip.yml

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Original PR URL: langgenius#30251