Add explicit permissions to GitHub Actions workflow for security

Co-authored-by: rvosa <106490+rvosa@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -12,6 +12,11 @@ jobs:
     name: Build and Test treebase-core
     runs-on: ubuntu-latest
 
+    permissions:
+      contents: read
+      checks: write
+      pull-requests: write
+    
     steps:
     - name: Checkout code
       uses: actions/checkout@v4