Actually delete the correct upgrade transient

Author: danielbachhuber

src/WP_CLI/CommandWithUpgrade.php

@@ -532,9 +532,9 @@ static function ( $result ) {
 	// phpcs:ignore PSR2.Methods.MethodDeclaration.Underscore -- Whitelisting to provide backward compatibility to classes possibly extending this class.
 	protected function _list( $_, $assoc_args ) {
 
-		// If `--force-check` flag is present, delete the ${item_type} transient.
+		// If `--force-check` flag is present, delete the upgrade transient.
 		if ( true === (bool) Utils\get_flag_value( $assoc_args, 'force-check', false ) ) {
-			delete_site_transient( $this->item_type . 's' );
+			delete_site_transient( $this->upgrade_transient );
 		}
 
 		// Force WordPress to check for updates if `--skip-update-check` is not passed.