ci: add a concurrency group to the CI workflow

[lvaroqui]

Add a concurrency group to the CI workflow, keyed on workflow and ref.

Pushing several times to a pull request currently leaves every older CI run going, which uses runner time on results nobody will look at. With this change, a new run on a pull request cancels the one already in progress for that ref. Pushes to main and manual dispatches are never cancelled, so every commit on main still gets a full CI result.

The merge_group check in cancel-in-progress does nothing for now, because the workflow doesn't listen for merge_group events. It is there so the behavior stays correct if a merge queue is turned on later.

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Adds concurrency control to the CI workflow.

This PR appears safe to merge.

What we checked:

• Running main CI stays alive: The cancel-in-progress expression is false for push and manual events. These events may replace pending runs, but they do not cancel running ones.

Summary

Adds a concurrency group to .github/workflows/ci.yml, keyed by workflow and ref.

• New pull request runs cancel older runs for the same pull request.
• Push and manual events do not cancel running CI.
• lvaroqui accepted skipping intermediate pending runs as intended, while preserving runs already in progress.
• No new actionable issues were found.

_{Reviews (2) · Last reviewed commit: "ci: add a concurrency group to the CI wo..." · Reviewed by Greptile}

[codspeed]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 31 untouched benchmarks
⏩ 6 skipped benchmarks¹

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_{Comparing enable-concurrency-group-in-ci (04a7991) with main (8c84fcc)}

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩