Undo code style change in $config_extra_php

This unnecessarily broke cron-command tests

Author: swissspidy

features/testing.feature

@@ -13,7 +13,7 @@ Feature: Test that WP-CLI loads.
     Given a WP install
     And the wp-config.php file should contain:
       """
-      if ( defined( 'DISABLE_WP_CRON' ) === false ) { define( 'DISABLE_WP_CRON', true ); }
+      if ( ! defined( 'DISABLE_WP_CRON' ) ) { define( 'DISABLE_WP_CRON', true ); }
       """
     And a test_cron.php file:
       """

src/Context/FeatureContext.php

@@ -1592,7 +1592,7 @@ public function install_wp( $subdir = '', $version = '' ): void {
 		$subdir = $this->replace_variables( $subdir );
 
 		// Disable WP Cron by default to avoid bogus HTTP requests in CLI context.
-		$config_extra_php = "if ( defined( 'DISABLE_WP_CRON' ) === false ) { define( 'DISABLE_WP_CRON', true ); }\n";
+		$config_extra_php = "if ( ! defined( 'DISABLE_WP_CRON' ) ) { define( 'DISABLE_WP_CRON', true ); }\n";
 
 		if ( 'sqlite' !== self::$db_type ) {
 			$this->create_db();