Fix correct server root path SanityCheck.php

[gerasart]

we got issue where server root path has inccorect folder like

.../ca/site

but need that detect real root path like

../ca

and comaprison then works inccorect here

if (!(strpos($input, $beginsWith) === 0)) {

because - $input - correct symlink path
root project path - $beginsWith - incorrect.

please check on your side, my changes should works for all.

[gerasart]

or maybe we need add some custom filter, that we can change it from extened plugin.