When running under PHP 8.2, if an SMTP server is specified in LocalSettings.php using $wgSMTP, this deprecation warning is generated when sending an email (and is no longer silenced by MediaWiki since 9a2fac1e47c0d076). The PEAR Mail fix has already been merged upstream and is planned for an upcoming 1.5.1 release.
Upstream pull request: https://github.com/pear/Mail/pull/22
Upstream commit: https://github.com/pear/Mail/commit/11b5eeea6c60d10dca21053b60df19a8503b1402