GitHub Workflows security hardening (#7883)

.github/workflows/ci.yml

@@ -1,5 +1,7 @@
 name: CI
 on: [push, pull_request]
+permissions:
+  contents: read # to fetch code (actions/checkout)
 jobs:
   Tests:
     runs-on: ${{ matrix.os }}

.github/workflows/docs.yml

@@ -7,6 +7,8 @@ on:
     paths:
       - site/content/**
 
+permissions: {}
+
 jobs:
   release:
     name: Deploy docs