Improve code clarity based on code review feedback

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

Author: Copilot

src/WP_CLI/CommandWithUpgrade.php

@@ -215,8 +215,11 @@ public function install( $args, $assoc_args ) {
 
 				// Check if this is a WordPress.org plugin/theme directory URL.
 				// If so, extract the slug and treat it as a repository installation.
-				if ( preg_match( '#^https?://wordpress\.org/(plugins|themes)/([^/]+)/?#', $slug, $matches ) ) {
-					$slug      = $matches[2];
+				// Pattern matches: https://wordpress.org/plugins/plugin-slug/ or https://wordpress.org/themes/theme-slug/
+				// Capture group 1: type (plugins|themes)
+				// Capture group 2: slug (the plugin or theme slug name)
+				if ( preg_match( '~^https?://wordpress\.org/(plugins|themes)/([^/]+)/?~', $slug, $matches ) ) {
+					$slug      = $matches[2]; // Extract the slug.
 					$is_remote = false;
 					WP_CLI::log( sprintf( 'Detected WordPress.org %s directory URL, using slug: %s', $matches[1], $slug ) );
 				}