ci: Limit coverage job GITHUB_TOKEN permissions

Author: fabisev

.github/workflows/runtime-interface-client_merge_to_main.yml

@@ -95,6 +95,8 @@ jobs:
   # made every merge commit look ~0.4% lower than its own PR base, failing the
   # codecov/project status on identical code.
   coverage:
+    permissions:
+      contents: read
     strategy:
       fail-fast: false
       matrix: