Test against PHP8.4

This makes it possible to find issues that need to be fixed before a PHP8.4 release

Author: heiglandreas

.github/workflows/integration.yml

@@ -22,6 +22,9 @@ jobs:
           - php: 8.3
             buildphar: true
             experimental: false
+          - php: 8.4
+            buildphar: false
+            experimental: true
     env:
       PHAR: build/phar/captainhook.phar