[Bug] Step 2 workflow becomes deleted after concurrent runs during PR merge

[mynaoki]

Summary

Step 2 intermittently disappears from Actions and shows state=deleted via API, even though 2-collaborate.yml still exists.

Observed

• Step 1 completes successfully.
• Step 2 is triggered multiple times in parallel.
• Around PR merge timing, Step 2 disappears from Actions.
• API shows Step 2 as deleted.
• Workflow file is still present on main.

Expected

Workflow should be active or disabled_manually, not deleted, unless the file is removed.

Notes

• disable should not produce deleted.
• Adding concurrency to Step 2 reduced the issue in reproduction.