Update supported / tested PHP versions - add 8.3, drop 7.4, 8.0

• Drop testing of PHP versions no longer receiving security support
• Ref https://www.php.net/supported-versions.php (or https://endoflife.date/php)
• Previously: PHP version support - 7.4, 8.0, 8.1 (#108 - closed)
• Now we will test 8.1, 8.2, 8.3