ci: pin non-GitHub-owned GitHub Actions

[marten-seemann]

Pin non-GitHub-owned Actions to specific commit SHAs in CI workflows

Replaces floating major version tags (e.g. v4, v1, v9, v7) with pinned commit SHAs in benchmark.yml, clusterfuzz-lite-pr.yml, golangci-lint.yml, and test.yml. Each pinned SHA is annotated with a version comment for readability. This prevents supply chain attacks where a tag could be silently moved to a different commit.

^{Macroscope summarized e233545.}

[Copilot]

Pull request overview

Pins all non-GitHub-owned GitHub Actions used in this repository’s CI workflows to immutable commit SHAs (with version annotations), reducing the risk of supply-chain attacks from retagged/moved version tags.

Changes:

• Pin codecov/codecov-action in unit test workflow to a specific commit SHA.
• Pin golangci/golangci-lint-action in lint workflow to a specific commit SHA.
• Pin google/clusterfuzzlite actions and CodSpeedHQ/action in their respective workflows to specific commit SHAs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
.github/workflows/test.yml	Pins Codecov action to a commit SHA with a version comment.
.github/workflows/golangci-lint.yml	Pins golangci-lint GitHub Action to a commit SHA with a version comment.
.github/workflows/clusterfuzz-lite-pr.yml	Pins ClusterFuzzLite build/run actions to a commit SHA.
.github/workflows/benchmark.yml	Pins CodSpeed action to a commit SHA with a version comment.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 4 untouched benchmarks

---

_{Comparing gha-pin (e233545) with master (6e2278d)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.55%. Comparing base (6e2278d) to head (e233545).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #89   +/-   ##
=======================================
  Coverage   93.55%   93.55%           
=======================================
  Files           4        4           
  Lines         186      186           
=======================================
  Hits          174      174           
  Misses          6        6           
  Partials        6        6           

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