Description:
------------
Strict types seem to throw compile-time fatal error on retrieving data, if you pass integer in quotes. It defines string as integer.

I guess, it's working like this:
<?php
$string = '12345';
$arr = [$string => 1];
var_dump(array_keys($arr));

which returns:
array(1) {
    [0] => int(12345)
}

Bug was discovered after clear php install, no ini files was edited.

Test script:
---------------
<?php
declare(strict_types=1);
class Test {
	private $storage = [];
	public function setData(string $key, int $value): void
	{
		$this->storage[$key] = $value;
	}
	public function getAllData(): array 
	{
		return array_keys($this->storage);
	}
}

$test = new Test;
$test->setData('key', 1);
$test->setData('123', 2);
foreach ($test->getAllData() as $data) {
	echo gettype($data) . "\n";
}

Expected result:
----------------
string string

Actual result:
--------------
string integer