ci: run tests with PHP 8.4

.github/workflows/tests.yaml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-versions: ['8.2', '8.3']
+        php-versions: ['8.2', '8.3', '8.4']
     env:
       GOEXPERIMENT: cgocheck2
       GOMAXPROCS: 10