Minimize GITHUB_TOKEN permissions

Refs: https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token

Author: taiki-e

.github/workflows/ci.yml

@@ -1,5 +1,8 @@
 name: CI
 
+permissions:
+  contents: read
+
 on:
   pull_request:
   push:
@@ -94,6 +97,10 @@ jobs:
           RUSTFLAGS: ${{ env.RUSTFLAGS }} -Z randomize-layout
 
   security_audit:
+    permissions:
+      checks: write
+      contents: read
+      issues: write
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3

.github/workflows/release.yml

@@ -1,5 +1,8 @@
 name: Release
 
+permissions:
+  contents: write
+
 on:
   push:
     tags: