Potential fix for code scanning alert no. 126: Workflow does not contain permissions

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Signed-off-by: John Detter <4099508+jdetter@users.noreply.github.com>

Author: jdetter

.github/workflows/ci.yml

@@ -525,6 +525,8 @@ jobs:
           fi
 
   unity-testsuite:
+    permissions:
+      contents: read
     runs-on: spacetimedb-new-runner
     container:
       image: localhost:5000/spacetimedb-ci:latest