update: set explicit permissions for GitHub workflows - release-builds (#3390)

See #3386
CC @FranzBusch @ktoso @Lukasa

Signed-off-by: Melissa Kilby <mkilby@apple.com>

Author: incertum

.github/workflows/release_builds.yml

@@ -102,6 +102,9 @@ on:
         description: "Environment variables for Windows jobs as JSON (e.g., '{\"DEBUG\":\"1\",\"LOG_LEVEL\":\"info\"}')."
         default: "{}"
 
+permissions:
+  contents: read
+
 jobs:
   construct-matrix:
     name: Construct release build matrix