CI: set explicit permission

https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#permissions

Author: larabr

.github/workflows/tests.yml

@@ -10,6 +10,7 @@ jobs:
   tests:
     name: Tests
     runs-on: ubuntu-latest
+    permissions: {}
 
     steps:
     - uses: actions/checkout@v4