CI: Reduce action permissions per best practices

Author: wsnyder

.github/workflows/build.yml

@@ -1,3 +1,4 @@
+---
 # DESCRIPTION: Github actions config
 #
 # This file ONLY is placed under the Creative Commons Public Domain, for
@@ -10,7 +11,10 @@ on:
   push:
   pull_request:
   schedule:
-    - cron: '0 0 * * 0' # weekly
+    - cron: '0 0 * * 0'  # weekly
+
+permissions:
+  contents: read
 
 jobs:
   vlt: