External Libraries: Upgrade PHPMailer to version 6.9.3.
This is a maintenance release, adding support for the release version of PHP 8.4, and experimental support for PHP 8.5.
References:
* [https://github.com/PHPMailer/PHPMailer/releases/tag/v6.9.3 PHPMailer 6.9.3 release notes]
* [https://github.com/PHPMailer/PHPMailer/compare/v6.9.2...v6.9.3 Full list of changes in PHPMailer 6.9.3]
Follow-up to [50628], [50799], [51169], [51634], [51635], [52252], [52749], [52811], [53500], [53535], [53917], [54427], [54937], [55557], [56484], [57137], [59246].
Props desrosj, yogeshbhutkar, ayeshrajans.
Fixes #62632.
Built from https://develop.svn.wordpress.org/trunk@59481
git-svn-id: http://core.svn.wordpress.org/trunk@58867 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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