chore: Use ubuntu-slim for lightweight jobs (#167)

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/pr.yaml

@@ -4,7 +4,7 @@ on:
       - main
 jobs:
   build:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     permissions: {}
     steps:
       - run: echo "Hello, World"

.github/workflows/update-infrastructure-repo.yaml

@@ -55,7 +55,7 @@ on:
 jobs:
   update-infrastructure:
     name: Update Infrastructure
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     strategy:
       matrix:
         include: ${{ fromJSON(inputs.environment-matrix-json) }}