Revert "Remove conditional inclusion"

This reverts commit 30afdc5.

Author: swissspidy

utils/make-phar.php

@@ -230,7 +230,6 @@ function get_composer_versions( $current_version ) {
 		->in( WP_CLI_VENDOR_DIR . '/nb/oxymel' )
 		->in( WP_CLI_VENDOR_DIR . '/psr' )
 		->in( WP_CLI_VENDOR_DIR . '/seld' )
-		->in( WP_CLI_VENDOR_DIR . '/marc-mabe/php-enum' )
 		->in( WP_CLI_VENDOR_DIR . '/justinrainbow/json-schema' )
 		->in( WP_CLI_VENDOR_DIR . '/gettext' )
 		->in( WP_CLI_VENDOR_DIR . '/mck89' )
@@ -246,6 +245,11 @@ function get_composer_versions( $current_version ) {
 		->exclude( 'composer/composer/src/Composer/Question' )
 		->exclude( 'composer/composer/src/Composer/Repository/Pear' )
 		->exclude( 'composer/composer/src/Composer/SelfUpdate' );
+
+	// required by justinrainbow/json-schema v6+.
+	if ( is_dir( WP_CLI_VENDOR_DIR . '/marc-mabe/php-enum' ) ) {
+		$finder->in( WP_CLI_VENDOR_DIR . '/marc-mabe/php-enum' );
+	}
 }
 
 foreach ( $finder as $file ) {