PunyencodeAddressTest: set proper run requirements
PunyencodeAddressTest: set proper run requirements

The "fakefunctions" are all nice and dandy to get past the `idnSupported()` check, but if either of these functions is not _really_ available and therefore doesn't behave as expected, the test would still fail as the expected output of the `PHPMailer::punyencodeAddress()` function would not match.

In other words, this test should not use the `fakefunctions`, but should have a hard requirement for the `mbstring` extension (for the `mb_check_encoding()` and the `mb_convert_encoding()` function calls) and a check for the `idn_to_ascii()` function.

PHPMailer/PHPMailer,jimjag/PHPMailer,jimjag/PHPMailer,nawawi/PHPMailer,nawawi/PHPMailer,PHPMailer/PHPMailer