Treat empty unittest discovery as release skip

scripts/check-release-integration.sh

@@ -44,11 +44,20 @@ run_step() {
 
 run_discovered_tests() {
   local suite_dir="$1"
+  local status
   if ! find "$suite_dir" -type f -name 'test*.py' -print -quit | grep -q .; then
     echo "No unittest test files found under $suite_dir; skipping."
     return 0
   fi
+  set +e
   "$PYTHON" -m unittest discover -s "$suite_dir"
+  status=$?
+  set -e
+  if [[ "$status" == 5 ]]; then
+    echo "No unittest tests discovered under $suite_dir; skipping."
+    return 0
+  fi
+  return "$status"
 }
 
 run_step "Validate release refs and installed package metadata"