Add explicit permissions to GitHub Actions workflow for security

Co-authored-by: mihow <158175+mihow@users.noreply.github.com>

Author: Copilot

.github/workflows/test-slurm-jobs.yml

@@ -20,6 +20,8 @@ on:
 jobs:
   test-slurm-environment:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
 
     steps:
       - name: Checkout code