修复远程一对一关联到同一对象时仅成功最后一个的问题

[maoxuner]

修复远程关联一对一问题 https://github.com/top-think/framework/issues/2690

$keys = [1 => 1, 2 => 1];
$keys = array_flip($keys);
print_r($keys); // [1 => 2]