Add explicit permissions to Debian workflow for security

Co-authored-by: osorensen <21175639+osorensen@users.noreply.github.com>

Author: Copilot

.github/workflows/debian-cran-check.yaml

@@ -11,6 +11,8 @@ on:
 jobs:
   check-cran-debian:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     container:
       image: ghcr.io/r-devel/rcheckserver/debian:latest