chore: Use ubuntu-slim for lightweight jobs (#104)

This PR was automatically generated by a codemod implemented in the
following PR:
- coopnorge/codemod#321

ref: coopnorge/cloud-platform-team#1220

Author: pravindahal

.github/workflows/build.yaml

@@ -5,6 +5,6 @@ concurrency:
   cancel-in-progress: true
 jobs:
   build:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     steps:
       - run: echo hello world