update: set explicit permissions in GitHub workflows (2/2) (#152)

PR 2: See #150

CC @FranzBusch, @ktoso 

It may not have been necessary to separate this PR, but since it’s the
initial wave of refactoring, I wanted to be more cautious.

Signed-off-by: Melissa Kilby <[email protected]>

Author: incertum

.github/workflows/main.yml

@@ -6,6 +6,9 @@ on:
   schedule:
     - cron: "0 8,20 * * *"
 
+permissions:
+  contents: read
+
 jobs:
   unit-tests:
     name: Unit tests