Add permissions to GitHub actions

- Included permissions for the action. https://github.com/ossf/scorecard/blob/main/docs/checks.md#token-permissions

Setting token permissions to read-only follows the principle of least privilege. This is important because attackers may use a compromised token with write access to push malicious code into the project.

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#permissions

.github/workflows/go.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches: [ master ]
 
+permissions:
+  contents: read
+
 jobs:
 
   lint: