Improve maintainability by using slug_key variable consistently

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

src/WP_CLI/CommandWithTranslation.php

@@ -132,7 +132,7 @@ public function update( $args, $assoc_args ) {
 
 					// Capture data for formatted output (skip for summary format).
 					if ( $format && 'summary' !== $format ) {
-						$slug_value = 'core' === $obj_type ? $update->Version : $update->slug;
+						$slug_value = 'version' === $slug_key ? $update->Version : $update->slug;
 						$results_data[] = array(
 							$slug_key  => $slug_value,
 							'language' => $update->language,