fix: incomplete type for Builder::from property

[sebj54]

Hi,

I fixed an incorrect type in Illuminate\Database\Builder. PHPStan is showing a warning when I'm checking the from property of my Builder is an Expression.

You can see here that it can be an expression:

framework/src/Illuminate/Database/Query/Builder.php

Line 335 in 6c27ca4

$this->from = new Expression($expression);