test(zsh): check capture for fzf exit status in widget

[LangLangBart]

fix #4871

• first add a regression test => let it run to see only perl fails
• commit the suggested fix

Contribution Policy

We do not accept pull requests generated primarily by AI without genuine understanding or real-world usage context.

All contributions are expected to demonstrate:

• A clear understanding of the codebase
• Alignment with product direction
• Thoughtful reasoning behind changes
• Evidence of real-world usage or hands-on experience with the problem

If these expectations are not met, we would prefer to implement the changes ourselves rather than spend time reviewing low-effort submissions.

---

Acknowledgement

• I confirm that this PR meets the above expectations and reflects my own understanding and real-world context.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[junegunn]

Thanks for handling this. Confirmed the test fails without the patch but passes with it.