GH Actions: update for the release of PHP 8.3

... which is expected later today.

Author: jrfnl

.github/workflows/test.yml

@@ -31,10 +31,11 @@ jobs:
           - '8.0'
           - '8.1'
           - '8.2'
+          - '8.3'
         experimental: [false]
 
         include:
-          - php: '8.3'
+          - php: '8.4'
             experimental: true
 
     name: "Test on PHP ${{ matrix.php }}"