ci: add PHP 8.4 testing

Author: owenvoke

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        php: ['8.2', '8.3']
+        php: ['8.2', '8.3', '8.4']
         dependency-version: [lowest, highest]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.os }} - ${{ matrix.dependency-version }}