php.yml: Test on newer PHP

Author: reedy

.github/workflows/php.yml

@@ -16,6 +16,9 @@ jobs:
           - "7.4"
           - "8.0"
           - "8.1"
+          - "8.2"
+          - "8.3"
+          - "8.4"
     steps:
       - name: Checkout
         uses: actions/checkout@v2