[12.x] Fix required and sometimes validation of Password rule

[mrvipchien]

This PR fixes an issue where using Password::required() or Password::sometimes() inside an array of rules results in incorrect validation behavior.

When defining validation rules like:

$request->validate([
    'password' => ['confirmed', Password::required()],
]);

with the following payload:

{
    "password": "123",
    "password_confirmation": "123"
}

the validation does not work as expected.
The root cause is that Password::required() returns an array, which conflicts when it is placed inside another rule array.

This PR updated Password::required() so that it returns the rule instance instead of an array. This ensures the rule works correctly when used inside array-based validation.