GH-51232: [CI] Update comment bot to prevent people being assigned things via "take" unless unassigned

[thisisnic]

Rationale for this change

Non-committers could assign themselves issues already assigned to people

What changes are included in this PR?

Only let "take" assign issues if the issue isn't assigned

Are these changes tested?

No

Are there any user-facing changes?

No

• GitHub Issue: [CI] Update comment bot to prevent people being assigned things via "take" unless unassigned #51232

[Copilot]

🟡 Changes recommended

The workflow still runs on PR comments (issue_comment applies to PRs too), so take can unintentionally assign pull requests unless the job is additionally gated to issues-only.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Updates Arrow’s GitHub comment bot (“take”) behavior and contributor docs so that self-assignment only occurs when an issue is currently unassigned, preventing accidental reassignment of already-owned issues.

Changes:

• Restrict the comment_bot.yml “Assign issue” job to run only when the issue has no assignee.
• Update developer documentation to clarify that take only works on unassigned issues.

File summaries

File	Description
docs/source/developers/bug_reports.rst	Clarifies that take only self-assigns unassigned issues.
CONTRIBUTING.md	Updates contributor guidance to match the new take behavior.
.github/workflows/comment_bot.yml	Adds an “unassigned only” guard to the take-based assignment job.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The workflow condition change directly addresses the reported issue and the accompanying documentation updates are consistent with the new behavior.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0 new
• Review effort level: Lite