ci: use slim Ubuntu runners (#256)

It will be more environmentally friendly and cheaper (at least for GitHub, because it's a public project and GitHub pays for it, not you)

GitHub blog post about new 1 vCPU runners: https://github.blog/changelog/2025-10-28-1-vcpu-linux-runner-now-available-in-github-actions-in-public-preview

Pricing (tl;dr: $0.002/min): https://docs.github.com/en/billing/reference/actions-runner-pricing

GitHub-hosted runners reference: https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#standard-github-hosted-runners-for--private-repositories

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ permissions:
 
 jobs:
   ci:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     timeout-minutes: 10
     steps:
       - name: Checkout

.github/workflows/deploy.yml

@@ -19,7 +19,7 @@ permissions: {}
 jobs:
   deploy:
     name: Deploy Docs
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     steps:
       - name: Checkout
         uses: actions/checkout@v5

.github/workflows/pr-title.yml

@@ -14,7 +14,7 @@ concurrency:
 jobs:
   lint-pr-title:
     name: Lint PR title
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     if: ${{ (github.event.action == 'opened' || github.event.changes.title != null) && github.actor != 'renovate[bot]' }}
 

.github/workflows/release.yml

@@ -12,7 +12,7 @@ concurrency:
 jobs:
   release:
     name: Release
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     permissions:
       id-token: write