tests.yml: a push run on main is never cancelled by the next landing, so every landing gets its own Linux result #592

Goal: every landing on main gets its own completed Linux run, so lanes no longer wait about 30 minutes between landings for main's push run.

What happens today

• .github/workflows/tests.yml groups runs by ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}, with cancel-in-progress: true.
• A push to main has no pull request number, so every push run on main shares the group tests-refs/heads/main. Each landing cancels the run on the main before it.
• From bump-leg.py: --dry-run gives the real run's answer, so --to an annotated tag's own id is peeled to the commit it names in both runs, and a pin layout the rewrite refuses is refused by the dry run too (#534, #438) #561 (7d9bec9) to openRepoShape --doctor says it writes nothing into the repository but a --placement-plan file you name, keeps its clone for the NEXT lines that name it, shows its synopsis description again, and refuses a second --placement-plan or a second path (#546) #580 (dd3f23a) on 2026-10-15, every push run on main ended cancelled. Nine PRs landed with no Linux run over their combination (lane 4 on docs/release-notes/v1.0.0.md: the v1.0.0 release notes, a draft for Brett to amend before he tags, saying what 1.0 contains and promises, how to pin it by commit, what changed on the way grouped by the five tracking areas, and every known limit as the input that triggers it and what the person sees (#472) #473, 2026-10-15T12:54Z).
• So the lanes agreed on docs/release-notes/v1.0.0.md: the v1.0.0 release notes, a draft for Brett to amend before he tags, saying what 1.0 contains and promises, how to pin it by commit, what changed on the way grouped by the five tracking areas, and every known limit as the input that triggers it and what the person sees (#472) #473 to wait for main's push run to finish before each landing, about 30 minutes per landing, with five lanes' PRs queued.

The change

• A push or workflow_dispatch run is grouped by its commit (github.sha), so no later landing cancels it. Each one finishes and is that landing's own result.
• A pull-request run keeps its per-PR group and cancel-in-progress, so a new push to a PR still cancels that PR's older run.
• One way to write it: group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}. Keep cancel-in-progress: true.

After it lands, lanes land as soon as their own gates pass, without waiting for main's previous push run. A red push run names the landing that broke main.

Filed by lane openRepoShape-3, which posts the landing order on #473 (Brett Heap's ruling 27).