GHA: add explicit permissions to license-check and pin-check jobs

Agent-Logs-Url: https://github.com/livekit-examples/cpp-example-collection/sessions/bf6c5bcf-16e7-41e2-8c68-51a4ddddf58b

Co-authored-by: stephen-derosa <40528896+stephen-derosa@users.noreply.github.com>

Author: Copilot

.github/workflows/builds.yml

@@ -17,10 +17,14 @@ jobs:
   license-check:
     name: License Check
     uses: ./.github/workflows/license_check.yml
+    permissions:
+      contents: read
 
   pin-check:
     name: Pin Check
     uses: ./.github/workflows/pin_check.yml
+    permissions:
+      contents: read
 
   build:
     strategy: