Improve GithubActions security

Author: n-rodriguez

.github/workflows/ci.yml

@@ -1,6 +1,8 @@
 ---
 name: CI
 
+permissions: {}
+
 on:
   push:
     branches:
@@ -20,6 +22,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v5
+        with:
+          persist-credentials: false
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
@@ -50,6 +54,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v5
+        with:
+          persist-credentials: false
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1