Configure your rector.php:

<?php

use PhpParser\Node\Expr\Cast\Double;
use Rector\Config\RectorConfig;
use Rector\Renaming\Rector\Cast\RenameCastRector;
use Rector\Renaming\ValueObject\RenameCast;

return RectorConfig::configure()
    ->withConfiguredRule(RenameCastRector::class, [
        new RenameCast(Double::class, Double::KIND_REAL, Double::KIND_FLOAT),
    ]);