Add PHP 8.3

Author: kenjis

.github/workflows/phpunit.yml

@@ -40,7 +40,7 @@ jobs:
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0', '8.1', '8.2']
+        php-versions: ['7.4', '8.0', '8.1', '8.2', '8.3']
         db-platforms: ['MySQLi', 'SQLite3']
         mysql-versions: ['5.7']
         dependencies: ['highest']