ci: add least-privilege workflow permissions (CodeQL)

.github/workflows/client-versions.yaml

@@ -4,6 +4,10 @@ on:
   workflow_dispatch:
   workflow_call:
 
+# Least-privilege default: this report only reads the repo to census notebooks.
+permissions:
+  contents: read
+
 jobs:
   analyze-client-versions:
     runs-on: ubuntu-latest

.github/workflows/pr.yaml

@@ -6,6 +6,10 @@ on:
     branches:
       - main
 
+# Least-privilege default: lint and notebook tests only read the repo.
+permissions:
+  contents: read
+
 jobs:
   lint:
     uses: './.github/workflows/lint.yaml'

.github/workflows/test-notebooks-all.yaml

@@ -9,6 +9,10 @@ on:
         default: 'docs'
         type: string
 
+# Least-privilege default: notebook validation and execution only read the repo.
+permissions:
+  contents: read
+
 jobs:
   validate-notebooks:
     runs-on: ubuntu-latest

.github/workflows/test-notebooks-changed.yaml

@@ -8,6 +8,10 @@ on:
         type: string
         default: 'main'
 
+# Least-privilege default: change detection and notebook execution only read the repo.
+permissions:
+  contents: read
+
 jobs:
   validate-notebooks:
     runs-on: ubuntu-latest