Harden GitHub workflows

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

.github/workflows/test.yml

@@ -21,16 +21,22 @@ on:
   schedule:
     - cron: '23 5 * * 4'
 
+permissions:
+  contents: read
+
 jobs:
   build:
 
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
 
     steps:
     - name: Checkout repository and submodules
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         submodules: recursive
+        persist-credentials: false
     - name: Build in container
       run: ./tests/build-in-docker.sh
     - name: Start emulation and test