ci: stop cancelling required-check runs on pull request edits

[ss-o]

Description

Commit Lint and Public Contract Impact run on edited (and label events) as well as synchronize. A push and a pull-request edit landing together started two runs for one head SHA, and the shared concurrency group cancelled one of them. The cancelled check runs for required contexts kept #594 BLOCKED while the same contexts had passed; re-running the two cancelled runs made it CLEAN.

This removes the concurrency group from both workflows, with a comment saying why, so every run finishes. Both finish in seconds, so a superseded run costs almost nothing. Any group would still cancel a same-SHA run: a running one with cancel-in-progress: true, a pending one without it. The edited and label triggers stay, because Validate PR Title, Validate Issue Link and the contract label policy depend on them.

This is a deliberate exception to the organization workflow contract's concurrency rule (section 3) for these two required, sub-minute workflows. The organization's reusable commit-lint has the same trigger and group shape.

Related issues

Closes #597

Type of change

• ci - CI/workflow change

Checklist

• Ordinary work targets next; only same-repository hotfixes target main
• A next to main promotion uses a merge commit and records both parent SHAs (not a promotion)
• Commit messages follow Conventional Commits format
• Any Co-authored-by trailer credits a real human, never a bot, AI agent, or automation
• I have read the contribution guidelines
• Existing tests pass (zsh -n zi.zsh / Trunk checks)
• Documentation updated if needed (no documentation describes these groups)

Local checks: actionlint on both files, trunk check on both files, zsh -f tests/ci-registration.zsh, zsh tests/public-contract-impact.zsh.

[ss-o]

Fallback review under ADR-0026: Copilot request not registered on 4562f9f

Findings

No blocking findings on this head.

• Removing the concurrency groups from commit-lint.yml and public-contract-impact.yml is correct for the failure in #597. Any group, with or without cancel-in-progress, can cancel a same-SHA run, and those cancelled required contexts blocked #594. The comment says so and stays accurate.
• Every check in both workflows still comes from the event payload and git; nothing depended on the group. The edited and label triggers stay, which Validate PR Title, Validate Issue Link and the contract label policy need.
• Untested assumption: with two finished runs on one SHA, GitHub uses the newest check run for each name, so a stale run (for example one validating the title before an edit) should not decide the merge state. Not observed on GitHub yet.
• This is a deliberate exception to section 3 of the organization workflow contract, recorded in the PR description.

Checks this rests on

actionlint and trunk check on both files; zsh -f tests/ci-registration.zsh; zsh tests/public-contract-impact.zsh; GitHub checks on this head.