CI: add least-privilege permissions to GitHub Actions workflows

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref }}
   cancel-in-progress: true
 
+permissions:
+  contents: read
+
 jobs:
   ci:
     name: 🧪 Test & lint

.github/workflows/initiate_release.yml

@@ -9,6 +9,10 @@ on:
         type: string
         pattern: "^[0-9]+\\.[0-9]+\\.[0-9]+$"
 
+permissions:
+  contents: write
+  pull-requests: write
+
 jobs:
   init_release:
     name: 🚀 Create release PR

.github/workflows/release.yml

@@ -6,6 +6,9 @@ on:
     branches:
       - main
 
+permissions:
+  contents: write
+
 jobs:
   Release:
     name: 🚀 Release

.github/workflows/scheduled_test.yml

@@ -6,6 +6,9 @@ on:
     # Monday at 9:00 UTC
     - cron: "0 9 * * 1"
 
+permissions:
+  contents: read
+
 jobs:
   test:
     environment: ci