Fix: anchor MasterCard credit-card pattern (missing ^ regressed in 94a79c033)

[nikkoenggaliano]

The MasterCard entry in CreditCard's BRAND_REGEX_LIST is the only one of the eight brand patterns missing a leading ^ anchor. Because of this, v::creditCard('MasterCard') accepts inputs that are not valid MasterCard numbers specifically, Luhn-valid digit strings longer than 16 digits whose trailing 16 digits match the MasterCard pattern.

use Respect\Validation\Validator as v;

// 16-digit MasterCard from the docs — correctly accepted
var_dump(v::creditCard('MasterCard')->isValid('5376747397208720')); // true (OK)

// 17-digit, Luhn-valid, NOT a MasterCard — wrongly accepted today
var_dump(v::creditCard('MasterCard')->isValid('05105105105105100')); // true (BUG; should be false and rejected? No?)

Self-contained demonstration (no Composer needed), mirroring evaluate() +
Luhn::isValid() and using the verbatim shipped regex:

input                | luhn  | shipped  | fixed   | expectation
--------------------------------------------------------------------------------
5376747397208720     | pass  | ACCEPT   | ACCEPT  | valid 16-digit MasterCard -> must ACCEPT
05105105105105100    | pass  | ACCEPT   | reject  | INVALID 17-digit number   -> must REJECT

Fix

- self::MASTERCARD => '/(5[1-5]|2[2-7])\d{14}$/',
+ self::MASTERCARD => '/^(5[1-5]|2[2-7])\d{14}$/',

Regression test

Add to providerForInvalidInput() in tests/unit/Validators/CreditCardTest.php (alongside the other $masternegatives):

[$master, '05105105105105100'], // 17-digit (over-long): regression for missing ^ anchor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.41%. Comparing base (7d833fb) to head (9d8e764).

Additional details and impacted files

@@            Coverage Diff            @@
##                3.1    #1774   +/-   ##
=========================================
  Coverage     99.41%   99.41%           
  Complexity     1020     1020           
=========================================
  Files           194      194           
  Lines          2387     2387           
=========================================
  Hits           2373     2373           
  Misses           14       14           

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