Playground CLI: Don't create /wordpress/wp-config.php on boot (#1407)

Prevents creating a `wp-config.php` file in WordPress document root.
Instead, creates it one level higher as WordPress falls back to loading
it from there.

Related to
#1398. Similar
to #1382 and
#1401.

## Testing instructions

Run `bun packages/playground/cli/src/cli.ts server --login` and confirm
it loads an installed WordPress.

packages/playground/cli/src/setup-wp.ts

@@ -122,7 +122,7 @@ async function prepareWordPress(php: NodePHP, wpZip: File) {
 
 	php.mv(wpPath, '/wordpress');
 	php.writeFile(
-		'/wordpress/wp-config.php',
+		'/wp-config.php',
 		php.readFileAsText('/wordpress/wp-config-sample.php')
 	);
 }