ci: introduce PHP 8.4 to pipeline (#72)

Author: chr-hertel

.github/workflows/pipeline.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: ['8.2', '8.3']
+        php: ['8.2', '8.3', '8.4']
         dependencies: ['lowest', 'highest']
     steps:
       - name: Checkout