Fix email sender address when notification_sender is not set

Dependencies

• [2] RX5IIZMT Use Email::MIME instead of Email::Simple

Change contents

• replacement in src/lib/Hydra/Helper/Email.pm at line 16
  [2.456]→[2.456:552](∅→∅)
  − my $sender = $config->{'notification_sender'} // (($ENV{'USER'} // "hydra") . "@" . $url);
  [2.456]

  [2.552]
  + my $sender = $config->{'notification_sender'} // (($ENV{'USER'} // "hydra") . "@" . hostname_long);