Description:
------------
The behaviour of the $depth parameter of json_encode() has changed when encoding objects.

On PHP 8.1, all three examples below successfully encode the input object, while
on PHP <= 8.0, json_encode() returns false as this exceeds the max depth.

Discussion: https://externals.io/message/116279
Demo: https://3v4l.org/DoG4A

If we replace the $a object with an empty array [], it works: https://3v4l.org/vFgh0

Test script:
---------------
// depth 1
$a = new \stdClass();

// depth 2
$b = new \stdClass();
$b->x = $a;

// depth 3
$c = new \stdClass();
$c->x = [$a];

var_export(json_encode($a, 0, 0)); echo "\n";
var_export(json_encode($b, 0, 1)); echo "\n";
var_export(json_encode($c, 0, 2));

Expected result:
----------------
'{}'
'{"x":{}}'
'{"x":[{}]}'

Actual result:
--------------
false
false
false