Description:
------------
<?php
$arr = [];
for ($i = 0; $i < 5000000; $i++) {
    $mct = microtime(true);
    $arr[$mct] = $mct;
}
print_r($arr);

Expected result:
----------------
<?php
$arr = [];
for ($i = 0; $i < 5000000; $i++) {
    $mct = microtime(true);
    $arr[$mct] = $mct;
}
print_r($arr);
// result 
Array
(
    [1624008537] => 1624008538
    [1624008538] => 1624008538.6062
)
Key is diffrent and value is diffrent of same variable.