ci: remove cancel-merged-pr-tests workflow

[CatherineSue]

Description

Problem

The Cancel Merged PR Tests workflow (introduced in #1530, YAML bug fixed in #1556) attaches two status checks — Cancel PR Test (SMG) and Cancel PR Test (MLX) — to every merged PR, regardless of whether there was anything to cancel. That UI noise outweighs the actual benefit (cancelling a handful of in-progress PR test jobs after merge).

The only viable trigger that avoids surfacing as a PR check would be push to main, but that just moves the noise to main's commit history — same problem, different surface.

Solution

Delete the workflow. PR test jobs that haven't completed by merge time will simply run to completion, costing a few minutes of extra GPU time per merged PR. That's an acceptable price for a cleaner PR UI.

The PR-level concurrency on pr-test-rust.yml / pr-test-mlx.yml is unaffected — pushing a new commit to an open PR still cancels the prior in-progress run.

Changes

• Delete .github/workflows/cancel-merged-pr-tests.yml.

Test Plan

• After merge, no new Cancel PR Test (SMG/MLX) checks will appear on subsequent merged PRs.
• Per-PR test cancellation on new commits (the normal concurrency behavior on pr-test-*.yml) is untouched.

Checklist

• `cargo +nightly fmt` passes — N/A, workflow-only change
• `cargo clippy --all-targets --all-features -- -D warnings` passes — N/A
• (Optional) Documentation updated
• (Optional) Please join us on Slack #sig-smg to discuss, review, and merge PRs

Summary by CodeRabbit

• Chores
  • Streamlined internal CI/CD workflow configuration to reduce unnecessary job cancellations during merged pull requests.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: e029f6ad-1043-4cfa-954b-5e8474c43ad8

📥 Commits

Reviewing files that changed from the base of the PR and between 67f1d47 and 381d2dd.

📒 Files selected for processing (1)

• .github/workflows/cancel-merged-pr-tests.yml

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📝 Walkthrough

Walkthrough

The pull request removes the .github/workflows/cancel-merged-pr-tests.yml GitHub Actions workflow file entirely, which previously automated the cancellation of in-progress CI runs when pull requests were merged to the main branch.

Changes

Cohort / File(s)	Summary
CI Workflow Cleanup .github/workflows/cancel-merged-pr-tests.yml	Workflow file deleted. Previously listened for pull_request closed events on main branch when merged, and cancelled gateway-tests and mlx-tests jobs via concurrency groups.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• lightseekorg/smg#1530: Inverse operation—adds the same cancel-merged-pr-tests.yml workflow to cancel in-progress gateway-tests/mlx-tests on merged PRs.
• lightseekorg/smg#524: Modifies GitHub Actions workflow triggers by removing pull_request-based behavior patterns.

Suggested labels

ci

Suggested reviewers

• key4ng
• slin1237
• XinyueZhang369

Poem

🐰 A workflow departs in silent grace,
No more cancellations to race,
Merged tests now flow free,
Simpler CI to be,
Cleanup brings joy to this place! ✨

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/silly-stonebraker-517804

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[claude]

Clean removal of a noisy CI workflow. No issues found — the per-PR concurrency cancellation on pr-test-*.yml is unaffected.