ci: add read permissions for GitHub token in CI workflow

Grant contents and pull-requests read permissions to the auto-generated
GITHUB_TOKEN to fix HTTP 403 errors when tests call the GitHub API's
releases/generate-notes endpoint.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: cgrindel

.github/workflows/ci.yml

@@ -16,6 +16,9 @@ name: Continuous Integration
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
+permissions:
+  contents: read
+  pull-requests: read
 jobs:
   all_ci_tests:
     runs-on: ubuntu-24.04