Add top level read only permission to workflows

Author: dhurley

.github/workflows/assertion.yml

@@ -39,6 +39,9 @@ on:
       ARTIFACTORY_URL:
         required: true
 
+permissions:
+  contents: read
+
 jobs:
   build-assertion-document:
     name: Create Assertion Document

.github/workflows/vulncheck.yml

@@ -14,6 +14,9 @@ on:
         required: false
         default: 'main'
 
+permissions:
+  contents: read
+
 jobs:
   vulncheck:
     name: Vulnerability Check