[PHP-WEBMASTER] [web-php] PR #1145: Update security.txt

Pull Request: Update security.txt by adoy · Pull Request #1145 · php/web-php · GitHub
Author: adoy

Updated security.txt expiration date as suggested by the release process following the announcement of the initial stable version of 8.4.

Cf: php-src/docs/release-process.md at master · php/php-src · GitHub