[5.8] Fix validation with multiple passes() calls

[staudenmeir]

Validation incorrectly passes after the first time if required isn't the first rule:

$v = Validator::make([], ['foo' => 'required|string']);
dump($v->passes()); // false
dump($v->passes()); // false

$v = Validator::make([], ['foo' => 'string|required']);
dump($v->passes()); // false
dump($v->passes()); // true

We have to reset the $failedRules property every time passes() gets called.

Fixes #28480.