[TASK] Temporarly skip mailer unit test execution with PHP8.1

Symfony recently released new version v5.4.12 and v6.1.4 of the
framework which contains a change in `symfony/mailer` throwing
a TransportException and passing null as 2nd ($code) argument.
This is deprecated since PHP8.1 and emits now a corresponding
depcreaction warning in some circumenstances and breaking one
mailer unit test.

See: https://github.com/symfony/symfony/issues/47402

This change temporarly skips the test for PHP8.1 until the fix
has been merged and released a new version by symfony.

Resolves: #98216
Releases: main, 11.5
Change-Id: I12a18f425bd573e1943dddad909c7c3256c1fd87
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75557


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>