ci: cancel in-progress shard runs on PR events to stop CI queue pile-up

[ooples]

Problem

sonarcloud.yml (the 49-shard test matrix) set cancel-in-progress: false for pull_request events. Every synchronize (and every master push) therefore stacked another full matrix in the queue instead of superseding the prior run. Against the GitHub free-tier 20-concurrent-job cap this saturated the pool for hours — fresh runs sat pending with 0 jobs dispatched, so PRs showed no shard checks running at all (observed live on PR #1789 and other open PRs).

Fix

Set cancel-in-progress: true for all events. The latest commit on a branch/PR is the only one whose green signal matters; superseding the stale in-flight run frees runners immediately so the current tip actually gets scheduled.

Trade-off (accepted): a mid-matrix cancel marks the superseded SHA's in-flight shards cancelled (which GitHub reports as failing) — but that is not the head. The freshly-triggered run for the new tip is the authoritative signal branch-protection / mergeability consume, and it runs to completion because nothing newer supersedes it.

Why this needs to land on master

For pull_request runs GitHub evaluates the workflow (and its concurrency) from the PR's merge commit (head ∪ base). Once master carries this fix, every other open PR picks it up on its next run/synchronize — unblocking the shard runs across all PRs, not just the one this was found on.

Single-file workflow change; no code impact.

🤖 Generated with Claude Code

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

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📥 Commits

Reviewing files that changed from the base of the PR and between 3522f76 and 2e243f4.

📒 Files selected for processing (1)

• .github/workflows/sonarcloud.yml

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/pr-shards-cancel-in-progress

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