PHP 8.2: fix deprecated use of "parent" in callables

Summary: Closes T15200

Test Plan:
Test 1:

I was able to run arc unit --everything without the error thrown from T15200

Test 2:

I also tried this and it still works:

php -a
require 'src/applications/metamta/exception/PhabricatorMetaMTAReceivedMailProcessingException.php';
$asd = new PhabricatorMetaMTAReceivedMailProcessingException("1", "TEST MESSAGE");
var_dump($asd->getMessage());

You get:

string(12) "TEST MESSAGE"

Reviewers: O1 Blessed Committers, Matthew

Reviewed By: O1 Blessed Committers, Matthew

Subscribers: speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15200

Differential Revision: https://we.phorge.it/D25099