Description:
------------
If an array containing values which are not strings is passed as
$from_encoding to mb_convert_encoding(), the array is modified
although it is not passed by reference.

This issue is fixed as of PHP 7.4.0.


Test script:
---------------
<?php
class Utf8Encoding
{
    public function __toString()
    {
        return 'UTF-8';
    }
}

$utf8encoding = new Utf8Encoding();
$encodings = [$utf8encoding];
var_dump($encodings);
mb_convert_encoding('foo', 'UTF-8', $encodings);
var_dump($encodings);
?>


Expected result:
----------------
array(1) {
  [0]=>
  object(Utf8Encoding)#1 (0) {
  }
}
array(1) {
  [0]=>
  object(Utf8Encoding)#1 (0) {
  }
}


Actual result:
--------------
array(1) {
  [0]=>
  object(Utf8Encoding)#1 (0) {
  }
}
array(1) {
  [0]=>
  string(5) "UTF-8"
}