ci: declare workflow-level contents: read on 1 workflows

Pins the default GITHUB_TOKEN to contents: read on workflows that don't
call a GitHub API beyond the initial checkout. Other workflows that need
write scopes are left implicit for a maintainer to declare.

Motivation: CVE-2025-30066 (March 2025 tj-actions/changed-files
compromise) exfiltrated GITHUB_TOKEN from workflow logs. Per-workflow
caps bound runtime authority irrespective of repo or org default,
give drift protection, and are credited per-file by the OpenSSF
Scorecard Token-Permissions check.

YAML validated locally with yaml.safe_load.

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

Author: arpitjain099

.github/workflows/docgen.yml

@@ -8,6 +8,9 @@ on:
   push:
     branches: [main]
 
+permissions:
+  contents: read
+
 jobs:
     build-docs:
         runs-on: linux.g5.4xlarge.nvidia.gpu