Add support for new 1vcpu ubuntu-slim runner label

[cestorer]

Per today's public preview release: https://github.blog/changelog/2025-10-28-1-vcpu-linux-runner-now-available-in-github-actions-in-public-preview/

Fixes #587

[muzimuzhi]

This is incomplete. More places need updates.

Please check out ea8e01d (Merge pull request #491 from ericcornelissen/runner-windows-2025, 2024-12-27) or 9f5e8de (add macos-15-intel runner label support, 2025-09-21).

I found no info about which version of Ubuntu ubuntu-slim uses, thus not sure how to add ubuntu-slim entry in defaultRunnerOSCompats.

actionlint/rule_runner_label.go

Lines 81 to 89 in 540883c

	var defaultRunnerOSCompats = map[string]runnerOSCompat{
	"ubuntu-latest": compatUbuntu2404,
	"ubuntu-latest-4-cores": compatUbuntu2404,
	"ubuntu-latest-8-cores": compatUbuntu2404,
	"ubuntu-latest-16-cores": compatUbuntu2404,
	"ubuntu-24.04": compatUbuntu2404,
	"ubuntu-24.04-arm": compatUbuntu2404,
	"ubuntu-22.04": compatUbuntu2204,
	"ubuntu-22.04-arm": compatUbuntu2204,

[rhysd]

I'll take a look at this PR within a few days.

[cestorer]

@muzimuzhi updated

I'm assuming 24.04, but unfortunately there is literally no documentation on that image. :/

[rhysd]

I confirmed the runner is Ubuntu 24.04.

$ lsb_release -a
Distributor ID:	Ubuntu
Description:	Ubuntu 2[4](https://github.com/rhysd/misc/actions/runs/19232713141/job/54974783604#step:3:5).04.3 LTS
Release:	24.04
Codename:	noble

[rhysd]

Thank you for catching this and I apologize for the late review.

[muzimuzhi]

I'm assuming 24.04, but unfortunately there is literally no documentation on that image. :/

FYI, https://github.com/actions/runner-images added ubuntu-slim image definition on Dec 13, 2025. See actions/runner-images#13423. While writing this, ubuntu-slim is still not listed in the "Available Images" README section.

According to the definition, yes ubuntu-slim is (currently) Ubuntu 24.04.

[jsoref]

Fwiw, actions/runner-images@0830eeb added ubuntu-slim to the "Available Images" README section.