fix bug in merge method of class Arr

$array1 = ['a' => 'x'];
$array2 = ['a' => [1, 2]];
Arr::merge($array1, $array2);
above code wiil throw exception: Argument 1 passed to Hyperf\Collection\Arr::merge() must be of the type array, string given, called in ...

src/Arr.php

@@ -569,11 +569,11 @@ public static function merge(array $array1, array $array2, bool $unique = true):
     {
         $isAssoc = static::isAssoc($array1 ?: $array2);
         if ($isAssoc) {
-            foreach ($array2 as $key => $value) {
-                if (is_array($value)) {
-                    $array1[$key] = static::merge($array1[$key] ?? [], $value, $unique);
+            foreach ($array2 as $key => $value2) {
+                if (is_array($value2) && isset($array1[$key]) && is_array($array1[$key])) {
+                    $array1[$key] = static::merge($array1[$key], $value2, $unique);
                 } else {
-                    $array1[$key] = $value;
+                    $array1[$key] = $value2;
                 }
             }
         } else {