Add casting

Author: swissspidy

src/Plugin_Command.php

@@ -404,6 +404,9 @@ public function activate( $args, $assoc_args = [] ) {
 
 				// If the error is due to unexpected output, display it for debugging
 				if ( 'unexpected_output' === $result->get_error_code() ) {
+					/**
+					 * @var string $output
+					 */ 
 					$output = $result->get_error_data();
 					if ( ! empty( $output ) ) {
 						WP_CLI::debug( "Unexpected output: {$output}", 'plugin' );