Add ubuntu-slim runner to CI

GitHub Actions 1 vCPU Linux runners are now in public preview. Customers
looking to run lightweight operations can take advantage of these lower
cost runners[^1]. This patch adds ubuntu-slim runner to the CI matrix.

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

Author: ikalnytskyi

.github/workflows/ci.yml

@@ -20,6 +20,7 @@ jobs:
     strategy:
       matrix:
         os:
+          - ubuntu-slim
           - ubuntu-22.04
           - ubuntu-22.04-arm
           - ubuntu-24.04
@@ -67,6 +68,7 @@ jobs:
     strategy:
       matrix:
         os:
+          - ubuntu-slim
           - ubuntu-22.04
           - ubuntu-22.04-arm
           - ubuntu-24.04
@@ -122,7 +124,7 @@ jobs:
           EXPECTED_SSL: true
 
   zizmor:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     permissions:
       security-events: write