Add: Set required contents read permission on cc workflow

To check for available conventional commits the workflow need to be able
to read the contents of the repository. For public repos this isn't
strictly required but maybe it elevates the permission for PRs from
externals.

.github/workflows/conventional-commits.yml

@@ -5,6 +5,7 @@ on:
 
 permissions:
   pull-requests: write
+  contents: read
 
 jobs:
   conventional-commits: