ci: add permissions block to smoke-tests workflow

Resolves CodeQL findings: workflow does not contain permissions.
Consistent with build.yml and pr.yml patterns in this repo.

Author: james-nesbitt

.github/workflows/smoke-tests.yaml

@@ -14,6 +14,9 @@ on:
   push:
     branches: [main]
 
+permissions:
+  contents: read
+
 jobs:
   smoke-modern:
     runs-on: ubuntu-latest