PHP array_walk function appends elements to a two-dimensional array

The array_walk function adds elements to a two-dimensional array

array_walk

$data = [
    [
        'a'=>1,'b'=>2,  
    ],
    [
        'c'=>3,'d'=>4,
    ]   
];
$arr = [
    'text'=>'text',
];

 array_walk($data, function (&$value, $key, $arr) {
                            $value = array_merge($value, $arr);
                        }, $arr);
 var_dump($data);