Fix when first insert value is array

[guram-vashakidze]

@pdphilip hello,

thank you merge my previous PR. I faced one issue in insert flow. For example my index has next mapping:

'field_foo' => [
    'type' => 'text'
],
'field_bar' => [
    'type' => 'text'
],

If I insert in this way:

$index = new MyIndexModel();
$index->fill(['field_bar' => 'Bar value', 'field_foo' => ['Foo value 1', 'Foo value 2']])->save();

It works. But if I use next way:

$index = new MyIndexModel();
$index->fill(['field_foo' => ['Foo value 1', 'Foo value 2'], 'field_bar' => 'Bar value'])->save();

It doesn't work, because first value is array and current insert starts use every value like independent inserted doc.
I changed it to check array_is_list - looks it solved the issue. There is I see just one problem - this function appeared after PHP 8.0, but I saw that last version of your lib supports Laravel upper then 10.0 (which needed PHP 8.0+)