CI: add explicit permissions block to clang-tidy workflow

Set minimal permissions (contents: read) as flagged by CodeQL.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/clang-tidy.yml

@@ -12,6 +12,9 @@ on:
     paths-ignore:
       - 'docs/**'
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: [runs-on, runner=16cpu-linux-x64, "run-id=${{ github.run_id }}", "extras=s3-cache"]