fix: ensure iam_config.json exists in setup target for CI

The GitHub Actions workflow calls 'make setup' which was not creating
iam_config.json, causing the server to start without IAM integration
enabled (iamIntegration = nil), resulting in NotImplemented errors.

Now 'make setup' copies iam_config.local.json to iam_config.json if
it doesn't exist, ensuring IAM is properly configured in CI.

test/s3/iam/Makefile

@@ -57,6 +57,10 @@ setup: ## Setup test environment
 	@echo "Setting up test environment..."
 	@mkdir -p test-volume-data/filerldb2
 	@mkdir -p test-volume-data/m9333
+	@if [ ! -f iam_config.json ]; then \
+		echo "Creating iam_config.json from iam_config.local.json..."; \
+		cp iam_config.local.json iam_config.json; \
+	fi
 
 start-services: ## Start SeaweedFS services for testing
 	@echo "Starting SeaweedFS services using weed mini..."