fix(ci): Change runner to ubuntu-slim for matrix

[janisz]

Description

• https://github.blog/changelog/2025-10-28-1-vcpu-linux-runner-now-available-in-github-actions-in-public-preview/

User-facing documentation

• CHANGELOG.md is updated OR update is not needed
• documentation PR is created and is linked above OR is not needed

Testing and quality

• the change is production ready: the change is GA, or otherwise the functionality is gated by a feature flag
• CI results are inspected

Automated testing

CI

[sourcery-ai]

Hey - I've left some high level feedback:

• Consider whether other jobs in this workflow (or related workflows) should also be switched to ubuntu-slim for consistency in environment and performance characteristics, or document why this particular job is different.
• Since ubuntu-slim is a preview 1-vCPU runner, double-check that all tools and system dependencies used by this job are available there; if any steps rely on preinstalled software from ubuntu-latest, you may need explicit setup steps.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider whether other jobs in this workflow (or related workflows) should also be switched to `ubuntu-slim` for consistency in environment and performance characteristics, or document why this particular job is different.
- Since `ubuntu-slim` is a preview 1-vCPU runner, double-check that all tools and system dependencies used by this job are available there; if any steps rely on preinstalled software from `ubuntu-latest`, you may need explicit setup steps.

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Central YAML (base), Organization UI (inherited)

Review profile: CHILL

Plan: Enterprise

Run ID: 0285c2fd-4a95-4c63-b266-ce4aeb677d94

📥 Commits

Reviewing files that changed from the base of the PR and between a91a065 and 753b7e3.

📒 Files selected for processing (1)

• .github/workflows/build.yaml

---

📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Updated CI/CD pipeline configuration for build optimization.

Walkthrough

The .github/workflows/build.yaml file is updated to change the runner image for the define-job-matrix job from ubuntu-latest to ubuntu-slim.

Changes

CI Runner Configuration

Layer / File(s)	Summary
Job matrix runner configuration .github/workflows/build.yaml	The define-job-matrix job runner selection changes from ubuntu-latest to ubuntu-slim.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: switching the CI runner from ubuntu-latest to ubuntu-slim for the matrix job.
Description check	✅ Passed	The description follows the required template with most sections present, including a reference to the GitHub changelog explaining the change, and notes that CI validation is the validation method.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch Change-runner-from-ubuntu-latest-to-ubuntu-slim

---

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

[github-actions]

🚀 Build Images Ready

Images are ready for commit 3d49ddb. To use with deploy scripts:

export MAIN_IMAGE_TAG=4.11.x-1015-g3d49ddb606

[davdhacs]

great idea! I wonder if there are other jobs we could put onto 1core -slim runners? This alone would help us to reduce our concurrency and be able to run more at once.

[janisz]

Yes they are some other jobs.
Release related jobs, periodic checks and nightly tags. Also there are some lint jobs that could be switch. The problem is that we need to run them to verify that everything is installed as slim has less packages so we may need to run steup-go/python/node to provide necessary software.