build: harden ccpp.yml permissions

Signed-off-by: Alex <[email protected]>

.github/workflows/ccpp.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches: [ master ]
 
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
 jobs:
   job:
     name: ${{ matrix.name }}-build-and-test