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
@@ -25,4 +27,4 @@ jobs:
           repo: 'svelte'
           branch: 'master'
           docs_path: 'site/content'
-          token: ${{ steps.github-app.outputs.token }}
+          token: ${{ steps.github-app.outputs.token }}