Show origin of warning in error message

[Naktibalda]

Fixes #6090

Codeception ErrorHandler wasn't very useful for investigating notices and warning, because it didn't show where the warning happened.

In ErrorHandler.php line 83:
                                     
  [PHPUnit\Framework\Exception (8)]  
  Undefined variable: file           
                                     

Exception trace:
  at /var/www/p2pr/vendor/codeception/codeception/src/Codeception/Subscriber/ErrorHandler.php:83
 Codeception\Subscriber\ErrorHandler->errorHandler() at /var/www/p2pr/vendor/codeception/module-symfony/

After applying this change, error message will tell the file and line of code where the warning originated.

[PHPUnit\Framework\Exception] Undefined variable: a at tests/unit/Codeception/Subscriber/ErrorHandlerTest.php:29